We used to fight in the holy battles in the company of the Prophet ﷺ and we had no wives with us. So we said, "O Messenger of Allah ﷺ! Shall we get castrated?" The Prophet ﷺ forbade us to do so.  

كُنَّا نَغْزُو مَعَ النَّبِيِّ ﷺ وَلَيْسَ لَنَا نِسَاءٌ فَقُلْنَا يَا رَسُولَ اللَّهِ أَلاَ نَسْتَخْصِي فَنَهَانَا عَنْ ذَلِكَ