From Sahih Bukhari (Hadith 2904):
Narrated `Umar:The properties of Bani An-Nadir which Allah had transferred to His Apostle as Fai Booty were not gained by the Muslims with their horses and camels. The properties therefore, belonged especially to Allah's Messenger (ﷺ) who used to give his family their yearly expenditure and spend what remained thereof on arms and horses to be used in Allah's Cause
Reference: Bukhari 2904