Saalim bin Ubaid As Shaji'i رضیﷲ عنه said: I saw Saydna Ali after the battle of Siffeen and he was holding my hand and we were walking near the army men died in the battle of Siffeen. Saydna Ali رضیﷲ عنه began asking forgiveness for them till we reached the people of Syria who died in the battle, So I said: O Ameerul Momineen! we're at the companions of Saydna Muawiya رضیﷲ عنه then Saydna Ali replied:
إنما الحساب علي وعلى معاوية
We, Muawiya and I, both will be held accountable for it.
[Kitab as Siffeen la ibn Dayzeel 134 #147, Tarikh Damishq 1/343]
Via حماد بن سعيد العلوي