The Messenger of Allah ﷺ ordered him to prepare an army, but the camels ran out. He then instructed him to take from the young camels designated for zakat, so he would take one camel in exchange for two, to be repaid from the zakat camels.
أن رسول الله ﷺ أمره أن يجهز جيشا، فنفدت الإبل، فأمره أن يأخذ في قلاص الصدقة، فكان يأخذ البعير بالبعيرين إلى إبل الصدقة.
It was narrated by Abu Dawud (3357), Daraqutni (3054), Hakim (2/56-57), and Bayhaqi (5/287-289), all through Hammad bin Salama, from Muhammad bin Ishaq, from Yazid bin Abu Habib, from Muslim bin Jubayr, from Abu Sufyan, from Amr bin Hurayth, from Abdullah bin Amr, and so on. Amr bin Hurayth is of unknown status, as stated in Taqrib, and the hadith hinges on him. There is also confusion in the chain regarding the order of narrators, for Hammad bin Salama narrated it this way, while Jareer bin Hazim narrated it from Muhammad bin Ishaq but placed Abu Sufyan before Muslim bin Jubayr. Ahmad narrated it (6593) in a longer context. Muhammad bin Ishaq is a mudallis, and I have not found an explicit statement from him confirming direct transmission.Bayhaqi said, "They differed over Muhammad bin Ishaq regarding his chain, and Hammad bin Salama gives the best account of it, and it has a sahih corroborating witness." By this he means a sahih path, namely what Daraqutni narrated (3052), and through his route Bayhaqi (5/287-289), from Ibn Wahb, from Ibn Jurayj, that Amr bin Shuayb informed him, from his father, from Abdullah bin Amr, and so on. This chain is hasan, and Bayhaqi treated it as a sahih corroborating witness for the preceding chain. Hafiz said in Fath al-Bari (4/489), Its chain is strong. Ibn Qayyim graded it hasan in Tahzib Sunan.Qilas is the plural of qalus, which is a young she-camel.On this subject there is also a narration from Abdullah bin Umar, who said, the Messenger of Allah said, "Do not sell one dinar for two dinars, nor one dirham for two dirhams, nor one measure of grain for two measures of grain, for I fear for you the practice of rima, and rima is riba." A man then stood up before him and said, "O Messenger of Allah, what do you say about a man who sells a horse for several horses, or a thoroughbred camel for several ordinary camels?" He said, "There is no harm in that, so long as it is exchanged hand to hand."This was narrated by Imam Ahmad (5885), from Husayn bin Muhammad, who said, Khalaf, meaning Ibn Khalifa, narrated to us, from Abu Janab, from his father, from Ibn Umar, and so on. Abu Janab's name is Yahya bin Abu Haya Kalbi, and his father is Abu Haya Kalbi, and both of them are unknown narrators. There are other chains for this hadith, weaker than this one.Malik also narrated it in Muwatta (2/634) through various routes from Umar bin Khattab, as his own statement rather than as a hadith from the Prophet.