The wealth of Banu Nadir was among what Allah had bestowed upon His Messenger as spoils which the Muslims had not gained by spurring on horse or camel. From it the Prophet ﷺ would spend on himself a year's provision, and whatever remained he would devote to cavalry and weapons as a preparation for the cause of Allah.
أخبرنا عبيد الله بن سعيد قال حدثنا سفيان عن عمرو يعني ابن دينار عن الزهري عن مالك بن أوس بن الحدثان
كانت أموال بني النضير مما أفاء الله على رسوله مما لم يوجف المسلمون عليه بخيل ولا ركاب فكان ينفق على نفسه منها قوت سنة وما بقي جعله في الكراع والسلاح عدة في سبيل الله
Bukhari narrated it in the Book of Jihad, chapter on the shield and one who shelters behind his companion's shield, no. 2904, and Muslim narrated it in the Book of Jihad, chapter on the ruling of war booty, no. 1757, from the hadith of Sufyan bin Uyayna, via this same chain.