From Sahih Muslim (Hadith 3406):
Sa'id b. al Musayyib heard Sa'd b. Abi Waqqas (Allah be pleased with him) saying that Uthman b. Maz'un decided to live in celibacy, but Allah's Messenger (ﷺ) forbade him to do so, and if he had permitted him, we would have got ourselves castrated
Reference: Muslim 3406