Musnad Ahmad 3:50

'Abd al-Samad narrated to us, my father narrated to me, al-Husayn—meaning al-Mu'allim—narrated to us, from Yahya—meaning Ibn Abi Kathir—, Abu Salamah informed me that 'Ata' ibn Yasar informed him that Zayd ibn Khalid al-Juhani informed him: That he asked 'Uthman ibn 'Affan, saying: "What is your opinion if a man has intercourse with his wife but does not ejaculate?" 'Uthman said: "He performs ablution as he performs ablution for prayer, and he washes his penis." And 'Uthman said: "I heard it from the Messenger of Allah, peace and blessings of Allah be upon him." So I asked 'Ali ibn Abi Talib, al-Zubayr ibn al-'Awwam, Talhah ibn 'Ubayd Allah, and Ubayy ibn Ka'b about that, and they commanded him to do that.