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 Messenger of Allah 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. (Using translation from Bukhārī 2904)
كَانَتْ أَمْوَالُ بَنِي النَّضِيرِ مِمَّا أَفَاءَ اللهُ عَلَى رَسُولِهِ ﷺ مِمَّا لَمْ يُوجِفِ الْمُسْلِمُونَ عَلَيْهِ بِخَيْلٍ وَلَا رِكَابٍ فَكَانَ رَسُولُ اللهِ ﷺ يَعْزِلُ نَفَقَةَ أَهْلِهِ سَنَةً ثُمَّ يَجْعَلُ مَا بَقِيَ فِي الْكُرَاعِ وَالسِّلَاحِ فِي سَبِيلِ اللهِ