Did some Companions—such as Abdullah ibn Amr ibn al-Aas and Al-Zubayr ibn Al-Awwam—leave Muawiya’s army after seeing Ammar ibn Yasir fighting with Ali’s army, believing that Muawiya’s army was the transgressing party? And how can Muawiya be considered a “Mujtahid” (one who exercises independent reasoning) who will receive one or two rewards, despite the Prophet describing his army as transgressing?

Firstly: Al-Zubayr ibn Al-Awwam did not live to encounter Mu'awiyah's army to abandon it, as he was killed before the Battle of Siffin. As for Abdullah ibn Amr ibn Al-Aas, he witnessed Siffin with Mu'awiyah but did not fight. He stated that his presence with Mu'awiyah was due to his obedience to his father, and he mentioned the Hadith "He will be killed by the renegade group" concerning Ammar ibn Yasir.

Secondly: a- The Hadith "He will be killed by the renegade group" does not explicitly state that Mu'awiyah's army is the intended renegade group. Ibn Taymiyyah interpreted it to mean those who killed him, and that many of Mu'awiyah's companions disapproved of Ammar's killing. b- Being a renegade does not expel one from faith. This is indicated by Allah's saying: (And if two parties of believers fight each other...), and the Prophet's (peace be upon him) naming the warring Muslim factions as "Muslims" in the Hadith of Al-Hasan ibn Ali. Mu'awiyah and his companions were striving in their fighting, as Mu'awiyah was demanding retribution for Uthman's blood, believing that Uthman's killers were in Ali's army. This ambiguity led a large number of companions to withdraw from fighting. Thus, it was a matter of ijtihad (independent reasoning), and the mujtahid (one who performs ijtihad) who errs is excused.