During the days of the Fitnah of the Sahaba (ra), the vast majority decided not to participate even if they leaned towards one side, yet they did this for many reasons, among them:
1- The narrations of the Prophet (SAWS) regarding the Fitnah were spreading at that time, they forbid participation.
2- The companions (ra) did Jihad against the Kouffar and weren’t taught to fight those who say “No god but Allah”.
3- The truth of the matter was not clear and the dust had not yet settled during the Fitnah, so it was very hard to identify which side to join.
But what we notice mainly is the following:
The Prophet (SAWS) was divinely appointed by Allah, so if he orders us to make Jihad, anyone who refuses to support him would be considered a Kaffir, as Allah ordered the Muslims to support him. On the other hand, the Shia claim that `Ali (ra) was divinely appointed by Allah thus supporting him is obligatory, so the same should apply to `Ali (ra), but what we read in the historical narrations shows that `Ali (ra) did not rule on the Kufr of those who did not participate, nor did he tell them that his support is obligatory like the prophets, nor did he punish or exile them… we provide some examples:
قال ابن الكلبيّ: كان سلمان اعتزل القتال في الفتنة هو وقوم ارتابوا بالقتال، فأقاموا بالرقّة، فكان عليّ يرسل إليهم الأعطية، ويقول: لا نمنعكم حقّكم من الفيء، لأنكم مسلمون، وإن امتنعتم من نصرتنا.
الإصابة في تمييز الصحابة ج3 ص116
[al-Kalbi said: Salman bin Thamamah and other folks had quit the fighting during the Fitnah because they feared its consequence, so they went to live in al-Raqqah and `Ali used to send them their shares and say: “We shall not prohibit you from your right of the war booty, because you are Muslims, even if you refrain from supporting us.”
source: al-Isabah fi Tamyeez al-Sahabah 3/116.]
قال عبد الله بن المغفل : فجلس عبد الله بن سلام على طريق علي بن أبي طالب حتى أتى عليه فقال : أين تريد ؟ قال : أريد العراق قال : لا تأت العراق وعليك بمنبر رسول الله صلى الله عليه وسلم فالزمه ،ولا أدري من ينجيك، فإن تركته لا تراه أبدا فقال من حوله : دعنا فلنقتله، فقال علي : دعوا عبد الله بن سلام فإنه منا رجل صالح.البغوي في معجم الصحابة ج4 ص104 رقم 1638 وعنه ابن حجرالعسقلاني في الإصابة في تمييز الصحابة ج4 ص: 119 وقال:اسناده جيد.
[`Abdullah bin Mughaffal al-Madani said: `Abdullah bin Salam stood in the way of `Ali ibn abi Talib until he came to him, so he told him: “Where are you headed?” he said: “I’m heading to `Iraq.” ibn Salam said: “Do not go to `Iraq, stick to the Mimbar of Rassul-Allah (SAWS), for if you leave it, you shall never see it.” so those around `Ali said: “Let us kill him!” `Ali then said: “Leave `Abdullah ibn Salam, he is from from us, a good man.”
sources: al-Baghawi in Mu`jam al-Sahaba 4/104 #1638, and from him in al-Isabah fi Tamyeez al-Sahaba 4/119.]
علي بن أبي طالب – رضي الله عنه- جاء -أيام الفتنة-إلى محمد بن مسلمة ، و قال له : (( ما خلفك عن هذا الأمر ؟ فقال له : دفع إلي ابن عمك -يعني الرسول – سيفا و قال لي : قاتل به ما قوتل العدو ، فإذا رأيت الناس يقتل بعضهم بعضا ، فاعمد به إلى صخرة فاضربه بها ، ثم ألزم بيتك حتى تأتيك منية قاضية ، أو يد خاطئة )) فقال علي خلّو عنه.
أحمد بن حنبل : ج 4 ص: 225
[During the days of Fitnah, `Ali ibn abi Talib (ra) came to Muhammad bin Maslamah (ra) and told him: “Why did you not join in this matter?” so he replied: “Your cousin -meaning the prophet (SAWS)- gave me a sword and said: Fight with it as long as the enemy is being fought, so if you see the people killing one another, then go to a big rock and break the sword, then stick to your house until death comes to you or you are killed.” so `Ali told them(his companions): “Leave him be.”
source: Musnad Ahmad 4/225.]