Musnad Ahmad 28:547

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Abu Sufyan al-Harashi narrated to me—and he was trustworthy, according to what the people of his land mentioned—from Muslim ibn Jubayr, the freed slave of Thaqif—and Muslim was a man from whom knowledge was taken, and he had lived during the time [of the Prophet] and heard [hadith]—from 'Amr ibn Hurayth al-Zubaydi, from 'Abdullah ibn 'Amr ibn al-'As, who said: I said: "O Abu Muhammad, we are in a land where we do not find the dinar or the dirham, and our wealth consists only of livestock. We trade them among ourselves, so we buy a cow for a sheep on credit until a specified term, and a camel for cows, and a horse for camels, all of that on credit. Is there any harm upon us in that?" He said: "You have come to one who is informed. The Messenger of Allah (peace and blessings of Allah be upon him) commanded me to send out an army using camels that I had. I mounted the people upon them until the camels ran out, and there remained a remainder of the people." He said: "So I said to the Messenger of Allah (peace and blessings of Allah be upon him): 'O Messenger of Allah, the camels have run out, and there remains a remainder of the people who have no mounts?'" He said: "The Messenger of Allah (peace and blessings of Allah be upon him) said to me: 'Purchase for us camels in exchange for young female camels from the camels of the Zakat, to be paid when they become due, so that we may send out this expedition.'" He said: "So I began to purchase a camel for two or three young female camels from the camels of the Zakat, to be paid when they became due, until I had sent out that expedition." He said: "Then, when the Zakat became due, the Messenger of Allah (peace and blessings of Allah be upon him) paid it."