Musnad Abu Ya'la al-Mawsili 6:100

Abu Ma'mar Isma'il ibn Ibrahim narrated to us, Ibrahim ibn Sa'd narrated to us, from Ibn Shihab, from Sa'id ibn al-Musayyib, who said: I heard Sa'd say: The Messenger of Allah (may Allah bless him and grant him peace) rejected celibacy for Uthman ibn Maz'un. And had he permitted it for him, we would have castrated ourselves.