Musannaf Ibn Abi Shaybah

Hazrat Umair bin Sa’d narrates that when Hazrat Ali (may Allah be pleased with him) returned from the Battle of Jamal and began preparations for Siffin, the people of the tribe of Nakha’ gathered and went to Ashtar. He asked, “Is there anyone in this house besides the people of the tribe of Nakha’?” They replied in the negative. He said, “Indeed, this group has killed its best men, and we advanced towards the people of Basra upon whom we had the right of allegiance, so with their breaking of the covenant, we were aided. Surely, soon you will march towards the people of Syria, upon whom you do not have the right of allegiance, so every man should see and carefully consider where he will wield his sword.”