Musannaf Ibn Abi Shayba 1:949

949. Abu Khalid al-Ahmar narrated to us, from Yahya ibn Sa'id, from 'Ubayd Allah ibn Ka'b, from Mahmud ibn Labid, who said: I asked Zayd ibn Thabit about a man who has intercourse but does not ejaculate. He said: "Upon him is the ghusl (full ritual bath)." I said to him: "Indeed, Ubayy used to not see that (as necessary)." He said: "Indeed, Ubayy retracted that before he died."