There are those whose sole purpose in their claims is to introduce doubt in the beliefs of the Muslims in order to draw them away from their iman toward a twisted heart and twisted mind, full of doubts, suspicions, and negative feelings. It is a quality of the Haqq that it has no likeness and is established on its own qualities and its own consistency. After much study and exposure to different people, I have come to the conclusion that the attack-point of choice for misguiding people, in order to separate them from the din, is the sahabah.
Why the 
sahabah, may Allah be pleased with them? Because to attack the worship of One Allah is something that will never be successful, neither in the hearts of Muslims or many non-Muslims. To attack the messenger of Allah, sallallahu'alayhi wa sallam, is pointless also, as his love is connected to the love of Allah, in as much as if one were to not love him, he wouldn't be amongst the ranks of the Muslims in the first place; furthermore, if any Muslim were to know of his 
mubarak sirah they would only increase in their love, until he became more dear to them than life itself.
In fact, to directly attack either of the two would be to inflame the 
ghayrah of a Muslim. An attack upon either would suddenly and clearly flag one as being a person of misguidance in the eyes of Muslims. It used to be that attacking the companions, may Allah be pleased with them, would be much of the same. However, a combination of a lack of knowledge as well as a lack of the companionship of the people of knowledge, coupled with an age in which anyone who considers anything as sacred is considered 'backwards' have all joined together to allow the poor and unsuspecting and unlearned lay-Muslim to let down his guard when an attack on the 
sahabah is near.
Once one allows poison to enter his or her heart about the companions of the messenger of Allah, sallallahu'alayhi wa sallam, know that to indict them is to cast a charge against the prophet, that his friends, followers, disciples, wives, children and family. It is really a charge against the prophet himself, may Allah save us from such a blasphemy and misguidance, because you can most surely know someone by knowing who they keep as company. This a stepping stone to the atheism that will surely follow, as one who doesn't believe in Muhammadun Rasulullah, cannot believe in La ilaha ill-Allah.
I know it may sound like a trite and bland topic, but had I not seen and heard of people losing their 
iman on the road of disrespecting the 
sahabah I would not make a point of writing this. The article below is a wonderful short essay written by Shaykh Taha Karan in Cape Town. Shaykh Taha graduated at the top of his class in Dar al-Ulum Deoband in India. He also spent time studying afterward in Egypt, and he runs one of the most intellectually active seminaries in South Africa, possibly the world. He shows by it, how, using a little bit of common sense, one can navigate through the strange and unbelievable types of doubts and whisperings that the people of misguidance throw at the people of belief in order to shake their sound faith in the teachings of Allah and His messenger, sallallahu'alayhi wasallam.
My request to my brothers and sisters in Islam is as follows. Firstly, you should try to read a book which tells about the companions, like 
The Men Around the Messenger of Allah and Shaykh Yusuf Kandehlawi's masterpiece work (which has been translated into okay English) 
Hayat al-Sahabah. Secondly, if anyone should whisper any sort of poison regarding even the smallest of matters regarding the 
sahabah into anyone's heart, then please call upon one of the noble people of learning or even this 
faqir in order to seek an antidote for the doubt that may linger after hearing something bad; maybe a God-fearing person can administer an antidote for whatever ails the hearts, as is the task with which Allah, Most High, dispatched them.
Finally, I would like to say that my comments are not aimed at any specific group or sect, rather towards the generality of people who don't have the utmost of love and respect for those who Allah, Himself, witnessed in His book, that He is pleased with them, in Surat al-Fath and other places. If anyone feels that this post or its attached article is aimed unfairly at them or their group, then let them ask themselves, "Do I love the companions of the messenger of Allah for the sake of Allah?" if the answer is yes, then rest assured that you are not the target of this article.
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Understanding Sayyiduna ‘Ali’s Absence from the  Campaigns of the First Three Khalifahs
                                                      
By Shaykh Taha Karaan
 Question: Why did  Hadhrat Ali (Radhiallaahu Anhu)                     not participate in  the wars during the ruling of the first 3                     Caliphs?  If Hadhrat Ali had no differences with the first                      three Khalifas, why did he not participate in any  battles that                     took place during their reigns,  particularly when Jihaad                     against the Kuffaar is  deemed a major duty upon the  Muslims?
 Was  salaam
 Answer:
 Respected Brother-in-Islam
 Assalaamu Alaykum Wa Rahmatullaahi Wa  Barakaatuhu
 The assumption underlying the question  is that since                     Sayyidunah Ali (Radhiallaahu Anhu) did  not  participate in the                    campaigns of the first 3  khulafa,  it can only mean that he was                    averse to  their rule,  perhaps even to the point of not                     recognising the  legitimacy of their rule.
 However, this  assumption can only be  accepted if one is                    prepared to  ignore the existence  of several historical facts                     which glare at the  objective observer from the pages of                     history. Some  of these are given here:
 1.  While Sayyiduna ‘Ali (Radhiallaahu  Anhu) might not                     physically have joined the  campaigns, he was at the side of                     the khalifah in  Madinah as a valued and trusted advisor – a                     position  that is by no means less important than being at  the                     battlefront. This is a fact documented in both  Sunni and Shi`i                     sources. “Nahj al-Balaghah”, for  example, records the  advice                    given by Sayyiduna ‘Ali  to Sayyiduna ‘Umar on  two occasions.                    The first one  appears as Sermon no.  133 and carries the                    heading “In  reply to ‘Umar ibn  al-Khattab who consulted him                     about taking part in  the battle against Byzantine”. The second                     is  numbered Sermond 145 and appears under the caption “Spoken                      when ‘Umar ibn al-Khattab consulted Amir al-Mu’minin  about                     taking part in the battle of Persia”. In both  instances  the                    advice given can clearly” be seen to be  aimed at  the success                    of the campaigns.
 2. It is also significant to note that  although Sayyiduna                     ‘Ali did not personally join the  armies on their  expeditions,                    he duly received his  share of the spoils  of war. Abu Ubayd has                    recorded  that Sayyiduna ‘Umar  fixed Sayyiduna ‘Ali’s share at                     5000 dirhams, and  gave both his sons Hasan and Husayn a                     similar share  of 5000. (“al-Amwal” p. 237) Another son of                     Sayyiduna  ‘Ali, namely Muhammad, was born to him from a  woman                     from Banu Hanifah who was brought to Madinah  as a war captive                     by Khalid ibn al-Walid after his  expedition against her tribe                     that had turned  apostate with Musaylamah. This woman  was given                    to  Sayyiduna ‘Ali by Sayyiduna Abu Bakr.  (“Tabaqat Ibn Sa’d”                     vol. 5 p. 67) and this Muhammad  is known in history as                     Muhammad ibn al-Hanafiyyah.
 3. If Sayyiduna ‘Ali’s not joining the  campaigns  of the                    three khulafa means that he was  averse to  their rule, how is                    one to interpret the  fact that  Sayyiduna Hasan and Sayyiduna                    Husayn both  took part  in the conquest of Tabaristan during the                     rule of  Sayyiduna ‘Uthman under Sa’id ibn al-’As in 30 AH?                      (See “Tarikh at-Tabari” vol. 5 p. 103, “al-Bidayah wan-Nihayah”                      vol. 5 p. 237)
 4. Furthermore, what  is one to make of  the fact that those                    of the Sahabah  upon whom the  Shi’ah took favourably as                    devotees of  Sayyiduna ‘Ali  and the Ahl al-Bayt unreservedly                    took  part in the  campaigns of Abu Bakr, ‘Umar and ‘Uthman?                     Here one  may speak of the following by way of example:
 SALMAN AL-FARISI took part in Sayyiduna  ‘Umar’s Persian                     campaign and played a crucial role  in the conquest of  Mada’in                    (“al-Bidayah wan-Nihayah”  vol. 5 pp.  135-140). He had also                    acted as governor  of Mada’in  for Sayyiduna ‘Umar (“al-Isabah”                    vol. 3  p. 113) and  used to actively encourage the military                     campaigns in  Syria by narrating ahadith on the virtues of                     jihad  (“Ansab al-Ashraf vol. 1 p. 488)
 HUDHAYFAH IBN  AL-YAMAN had played a  leading role in the                    conquest  of’Iraq. Like Salman,  he too had acted as governor                     for Sayyiduna ‘Umar  (“al-Isabah” vol. 1 p. 332), and later                     joined  military expeditions during the reign of Sayyiduna ‘Uthman.                      He is described by the Shi’i scholar, al-’Allamah  Ibn Mutahhar                     al-Hilli, as “one of the four pillars  amongst the  companions                    of Amir al-Mu’minin.” (“Jami’  ar-Ruwat”  vol. 1 p. 182)
 BILAL AL-HABASHI  joined the campaign in  Syria, either                    during the time  of Sayyiduna Abu Bakr  or Sayyiduna ‘Umar. He                    died in  Syria during the  reign of the latter Umar. (“al-Isabah”                     vol. 1 p.  171)*
 ‘AMMAR IBN YASIR took part  in the  campaign against                    Musaylamah in the time of  Sayyiduna  Abu Bakr. He fought                    valiantly, spurred on  the  Muslim forces, and lost his ear in                    this battle.   Later, during the reign of Sayyiduna ‘Umar, he                      accepted an appointment as the governor of Kufah under him. (“Tarikh                      al-Islam” vol. 2 p. 581}
 ABU  AYYUB AL-ANSARI is well known for  his participation in                     several battles, not least  amongst which was the expedition                     against  Constantinople led by Yazid in the time of his father                      Mu’awiyah. Abu Ayyub was martyred during this  expedition, and                     was buried under the walls of the  city. (“al-Bidayah  wan-Nihayah”                    vol. 5 p. 518)
 5. Apart from the above considerations,  one also  needs to                    keep in mind the sort of  relationship that  existed between                    Sayyiduna ‘Ali and  the khulafa before  him. This relationship                    is best  expressed in the fact  that he named 3 of his sons Abu                     Bakr, ‘Umar and  ‘Uthman. This is confirmed even by an avowedly                     Shi’i  source such as Shaykh Mufid’s “Kitab al-Irshad” (pp.                      268-269); and the fact that he married Umm Kulthum,  his                     daughter from Sayyidah Fatimah, to Sayyiduna  ‘Umar. (For a                     more detailed discussion of the  marriage of Umm Kultnum, see                      http://www.ansar.org/english/marriage.htm)
 All things considered, the assumption  that Sayyiduna ‘Ali                     did not take part in the  campaigns of the three  khulafa on                    account of his  differences with them,  diminishes into an                     incongruous aberration of  ridiculous proportions.