It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) appointed Sayyiduna Zayd bin Harithah (may Allah be pleased with him) as commander in the expedition of Mu'tah and said: "If Zayd is martyred, then Ja'far, and after Ja'far, Abdullah bin Rawahah will be the commander." Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: I too was in that expedition. We found Sayyiduna Ja'far (may Allah be pleased with him) slain, and on his body there were more than 90 wounds from swords and arrows.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16596