Khalid bin Samir reported,

Abdullah bin Rabah came to us, and I found that a group of people had gathered around him. He said, "Abu Qatada, the cavalryman of the Messenger of Allah ﷺ, narrated to us, saying, 'The Messenger of Allah ﷺ dispatched the army of the commanders and said, "Your commander is Zayd bin Haritha. If Zayd is struck down, then Jafar. If Jafar is struck down, then Abdullah bin Rawaha al-Ansari."'"Jafar leapt up and said, "By my father and mother, Prophet of Allah, I never feared that you would appoint Zayd over me."He replied, "Proceed, for you do not know which of these outcomes is better."The army set out and remained away as long as Allah willed. Then the Messenger of Allah ﷺ climbed the pulpit and ordered that the call be made, "Gather for prayer."The Messenger of Allah ﷺ said, "News has arrived" — or "News has come back," Abdul-Rahman was uncertain — "Shall I tell you about this fighting army of yours? They set out until they met the enemy. Zayd was struck down as a martyr, so seek forgiveness for him."The people sought forgiveness for him. Then he said, "Then Jafar bin Abu Talib took the banner and charged the enemy until he was killed as a martyr. I bear witness for him to the martyrdom, so seek forgiveness for him."Then he said, "Then Abdullah bin Rawaha took the banner and stood firm until he was struck down as a martyr, so seek forgiveness for him. Then Khalid bin Walid took the banner, though he was not one of the appointed commanders. He appointed himself."The Messenger of Allah raised his two fingers and said, "O Allah, he is a sword from Your swords, so grant him victory." Abdul-Rahman once said, "So bring victory through him."From that day Khalid was named the Sword of Allah. Then the Prophet ﷺ said, "Set out and reinforce your brothers, and let no one stay behind."So the people set out in intense heat, on foot and mounted.

عن خالد بن سمير قال

قدم علينا عبد الله بن رباح فوجدته اجتمع إليه ناس من الناس، قال: حدثنا أبو 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 على زيدا، قال: امضوا فإنك لا تدري أي ذلك خير. قال: فانطلق الجيش فلبثوا ماشاء الله، ثم إن رسول الله ﷺ صعد المنبر وأمر أن ينادى: الصلاة جامعة، فقال رسول الله ﷺ: ناب خبر- أو ثاب خبر، شك عبد الرحمن- ألا أخبركم عن جيشكم هذا الغازي، إنهم انطلقوا حتى لقوا العدو، فأصيب زيد شهيدا، فاستغفروا له. فاستغفروا له الناس، ثم أخذ اللواء جعفر بن أبي طالب فشد على القوم حتى قتل شهيدا، أشهد له بالشهادة، فاستغفروا له، ثم أخذ اللواء عبد الله بن رواحة، فأثبت قدميه حتى أصيب شهيدا فاستغفروا له، ثم أخذ اللواء خالد بن الوليد ولم يكن من الأمراء، هو أمر نفسه. فرفع رسول الله أصبعيه وقال: اللهم هو سيف من سيوفك فانصره- وقال عبد الرحمن مرة: فانتصر به. فيومئذ سمي خالد سيف الله، ثم قال النبي ﷺ: انفروا فأمدوا إخوانكم ولا يتخلفن أحد. فنفر الناس في حر شديد مشاة وركبانا.