Musnad Ahmad 2:90

Sufyan narrated to us, from ‘Amr and Ma’mar, from al-Zuhri, from Malik ibn Aws ibn al-Hadathan, from ‘Umar ibn al-Khattab, who said: The properties of Banu al-Nadir were among what Allah bestowed upon His Messenger (may Allah bless him and grant him peace) as spoils, for which the Muslims did not urge on any horses or camels. Thus, they were exclusively for the Messenger of Allah (may Allah bless him and grant him peace). He used to spend from them on his family for their annual provision—and he said once: their annual sustenance—and whatever remained, he would place it into the horses and weapons as equipment in the way of Allah, the Almighty and Majestic.