Sahih Muslim | Book 8 | Hadith Number 3238

Narrated by Sa'id b. al-Musayyib
Sa'id b. al-Musayyib reported: I heard Sa'd (b. Abi Waqqas) saying that the idea of 'Uthman b. Maz'un for living in celibacy was rejected (by the Holy Prophet), and if he had been given permission they would have got themselves castrated.