An indication of pardon for the Companions who fought in these events

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he said: "Indeed, this Ummah is an Ummah upon which is the special mercy of Allah Almighty; there will be no (general) punishment upon it (in the Hereafter, like that of the other nations that were destroyed), except the (trials and mutual bloodshed) which it brings upon itself." (The narrator says:) I asked: How will this Ummah punish itself? He said: "Was the Battle of the Camel not (a horror and) a punishment? Was the Battle of Siffin not a punishment? And was the battle that took place at Nahrawan not a punishment?"
Musnad Abi Ya'la: 4430; Allamah al-Haythami mentioned in Majma' al-Zawa'id that all the narrators of this hadith are thiqat (trustworthy), and Shaykh al-Albani declared it sahih (authentic).

It is narrated from a Companion (may Allah be pleased with him) from among the Muhajirun that the Messenger of Allah (peace and blessings be upon him) said: "The punishment of this Ummah has been decreed in the form of the sword (wielded among themselves), that is, mutual trial and fighting."
Imam Ahmad recorded it in his Musnad, and Allamah Nasir al-Din al-Albani declared it sahih (authentic).

It is narrated from Imam al-Zuhri (may Allah have mercy on him) that Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him), who is called by the honoured title "Dhu al-Shahadatayn" (the one of two testimonies), fought alongside Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) at the Battle of Siffin and engaged in combat against the enemy on his side.
Ishaq bin Rahwayh recorded it, and all its narrators are thiqat (trustworthy).