Abu Qatada reported,

The horseman of the Messenger of Allah ﷺ said, "The Messenger of Allah ﷺ dispatched the army of the commanders and said, 'Your commander is Zayd bin Haritha. If Zayd is killed, then Jafar. If Jafar is killed, then Abdullah bin Rawaha al-Ansari.'"Jafar leapt up and said, "May my father and mother be sacrificed for you, Prophet of Allah. I never feared that you would appoint Zayd over me."He replied, "Go forth, for you do not know which of these will turn out best."Then he mentioned the announcement of the deaths of Zayd, Jafar, and Abdullah bin Rawaha, then said, "Then Khalid bin Walid took up the banner, though he was not among the appointed commanders. He took command on his own initiative."The Messenger of Allah ﷺ raised his two fingers and said, "O Allah, he is a sword among Your swords, so grant him victory."

عن أبي قتادة

فارس رسول الله ﷺ قال: بعث رسول الله ﷺ جيش الأمراء وقال: عليكم زيد بن حارثة، فإن أصيب زيد فجعفر، فإن أصيب جعفر فعبد الله بن رواحة الأنصاري. فوثب جعفر فقال: بأبي أنت يا نبي الله وأمي، ما كنت أرهب أن تستعمل علي زيدا قال: امضوا فإنك لا تدري أي ذلك خير. ثم ذكر نعي زيد وجعفر وعبد الله بن رواحة ثم قال: ثم أخذ اللواء خالد بن الوليد، ولم يكن من الأمراء هو أمر نفسه فرفع رسول الله ﷺ أصبعيه وقال: اللهم هو سيف من سيوفك فانصره.