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  

The properties of Bam An-Nadir were among the booty that Allah gave to His Apostle such Booty were not obtained by any expedition on the part of Muslims, neither with cavalry, nor with camelry. So those properties were for Messenger of Allah ﷺ only, and he used to provide thereof the yearly expenditure for his wives, and dedicate the rest of its revenues for purchasing arms and horses as war material to be used in Allah's Cause. (Using translation from Bukhārī 4885)  

كَانَتْ أَمْوَالُ بَنِي النَّضِيرِ مِمَّا أَفَاءَ اللهُ عَلَى رَسُولِهِ ﷺ مِمَّا لَمْ يُوجِفِ الْمُسْلِمُونَ عَلَيْهِ بِخَيْلٍ وَلَا رِكَابٍ فَكَانَ يُنْفِقُ عَلَى أَهْلِهِ مِنْهَا نَفَقَةَ سَنَةٍ وَمَا بَقِيَ جَعَلَهُ فِي السِّلَاحِ وَالْكُرَاعِ عُدَّةً فِي سَبِيلِ اللهِ  

The wealth of Banu an-­Nadeer was among the fai' that Allah bestowed upon His Messenger ﷺ, for which the Muslims made no expedition with either cavalry or camelry (cf. al-Hashr 59:6). It was only for the Messenger of Allah ﷺ and he used to spend from it on his family's annual expenses-and on one occasion he said: his annual food supply ­-and what was left he spent on horses and weapons in preparation for jihad for the sake of Allah, may He be glorified and exalted, (Using translation from Aḥmad 171)   

أَنَّ «أَمْوَالَ بَنِي النَّضِيرِ مِمَّا أَفَاءَ اللهُ عَلَى رَسُولِهِ ﷺ مِمَّا لَمْ يُوجِفِ الْمُسْلِمُونَ عَلَيْهِ بِخَيْلٍ وَلَا رِكَابٍ وَكَانَتْ لِرَسُولِ اللهِ ﷺ خَالِصًا وَكَانَ يُنْفِقُ عَلَى أَهْلِهِ مِنْهَا نَفَقَةَ سَنَةٍ وَمَا بَقِيَ جَعَلَهُ فِي الْكُرَاعِ وَالسِّلَاحِ عُدَّةً فِي سَبِيلِ اللهِ»