Mukhtasar Bukhari

Narrated Abdullah bin Umar (may Allah be pleased with them): The Messenger of Allah (peace and blessings of Allah be upon him) appointed Zaid bin Harithah (may Allah be pleased with him) as the commander in the battle of Mu'tah, then said: "If Zaid is martyred, then Ja'far will be the commander, and if Ja'far is martyred, then Abdullah bin Rawahah will be the commander." Abdullah bin Umar (may Allah be pleased with them) says: I was present in that battle. When we searched for Ja'far bin Abi Talib (may Allah be pleased with him), we found him among the martyrs, and we saw more than ninety wounds of spears and swords on his body.