Musnad Ahmad 2:255

Sufyan narrated to us, from ‘Amr, from al-Zuhri, from Malik ibn Aws, who said: ‘Umar sent for me... and he mentioned the hadith, and said: "Indeed, the wealth of Banu al-Nadir was among that which Allah bestowed upon His Messenger as spoils, for which the Muslims did not urge on any horses or camels. He used to spend from it upon his family for their yearly provision, and whatever remained, he placed it into the horses and weapons as equipment in the way of Allah, the Almighty and Majestic."