(6) باب تَزْوِيجِ الْمُعْسِرِ الَّذِي مَعَهُ الْقُرْآنُ وَالإِسْلاَمُ
Narrated Ibn Masud:
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 Allah's Messenger (ﷺ)! Shall we get castrated?" The Prophet (ﷺ) forbade us to do so.
Reference: Sahih al-Bukhari 5071
In-book reference: Book 67, Hadith 9
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 7, Book 62, Hadith 9