Sahih Muslim Book 008, Hadith Number 3239.

Chapter: One who can support a wife should marry.

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 (May peace be upon him) forbade him to do so, and if he had permitted him, we would have got ourselves castrated.