Is what was mentioned true, that Uthman (may Allah be pleased with him) sent Ammar ibn Yasir to Egypt as part of a delegation to investigate the causes of unrest, and that Ammar did not return and joined the group of Ibn Saba?

The narrations concerning the Companion Ammar ibn Yasir's involvement in the Fitna are unanimously considered weak and unsound, and their meanings are contradictory. The narration mentioning Ammar's dispatch to Egypt and his winning over some of its people is weak in both its chain of transmission (sanad) and its text (matn). Its chain includes Saif ibn Omar al-Tamimi and Shu'aib ibn Ibrahim, both of whom are weak and unknown. As for its text, it is illogical; how can it be conceived that a great Companion like Ammar, with his precedence and experience, would be influenced by the words of unknown people and incite fitna against Uthman, may Allah be pleased with him?

There are other narrations, despite the weakness and discontinuity of their chains, which indicate that Ammar was reproaching Uthman. However, this reproach was not to the extent of inciting people or participating with the instigators of fitna in their objective. The disagreements among the Companions were based on their ijtihad (independent reasoning), not on seeking worldly gain or inciting against the Commander of the Faithful. The proof of his innocence from participating in the fitna is his absence from any role in the siege of Uthman, and the fact that the people of fitna did not rally around him.

Scholars have unanimously agreed that all the Companions are innocent of Uthman's blood, may Allah be pleased with him, and that those who abandoned him did not expect the matter to escalate to his killing; rather, they regretted what they had done.