Ibn Shihab (may Allah have mercy on him) narrates: Then the Messenger of Allah (peace and blessings be upon him) sent an army to Mu'tah and appointed Sayyiduna Zayd bin Harithah (may Allah be pleased with him) as its commander; if he was martyred, Ja'far bin Abi Talib would be their commander, and if Ja'far was martyred, Abdullah bin Rawahah would be their commander. So they set out until they met Ibn Abi Sabrah al-Ghassani at Mu'tah, where there were gatherings of Christian Arabs and Romans, and the (tribes of) Tanukh and Bahram were also there. Ibn Abi Sabrah shut the fortress against the Muslims for three days, then they (the enemy) came out, and they met on a field of green crops and fought fiercely. Sayyiduna Zayd bin Harithah (may Allah be pleased with him) took up the banner and was martyred, then Ja'far took it up and was martyred, then Ibn Rawahah took it up and was martyred. Then, after the commanders of the Messenger of Allah (peace and blessings be upon him), the Muslims agreed upon Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) (as their commander), and Allah defeated the enemy and gave the Muslims victory. The Messenger of Allah (peace and blessings be upon him) had sent them in Jumada al-Ula.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14029