Musnad Ahmad 916:1

Yahya ibn Adam narrated to us, he said: Zuhayr and Ibn Idris narrated to us, from Muhammad ibn Ishaq, from Yazid ibn Abi Habib, from Ma’mar ibn Abi Habibah, from Ubayd ibn Rifa’ah ibn Rafi’, from his father. Zuhayr said in his narration: Rifa’ah ibn Rafi’, and he was a participant of ‘Aqabah and Badr, said: I was with Umar, and it was said to him: "Indeed, Zayd ibn Thabit is issuing fatwas to the people in the mosque." Zuhayr said in his narration: "To the people according to his own opinion regarding the one who has intercourse but does not ejaculate." He said: "Bring him to me quickly." So he was brought. He said: "O enemy of himself! Have you reached the point where you issue fatwas to the people in the mosque of the Messenger of Allah, peace and blessings of Allah be upon him, based on your own opinion?" He said: "I did not do that, but my paternal uncles narrated to me from the Messenger of Allah, peace and blessings of Allah be upon him." He said: "Which of your uncles?" He said: "Ubayy ibn Ka’b." Zuhayr said: "And Abu Ayyub, and Rifa’ah ibn Rafi’." He turned to what this young man was saying—and Zuhayr said in his narration: "What is this boy saying?" I said: "We used to do it during the time of the Messenger of Allah, peace and blessings of Allah be upon him." He said: "Did you ask the Messenger of Allah, peace and blessings of Allah be upon him, about it?" He said: "We used to do it during his time, and we would not perform ghusl (ritual bath)." He said: So he gathered the people, and the people agreed that water (semen) is only from water (ejaculation), except for two men: Ali ibn Abi Talib and Mu’adh ibn Jabal. They both said: "If the circumcision [of the man] passes the circumcision [of the woman], then ghusl becomes obligatory." He said: Ali said: "O Commander of the Faithful, the most knowledgeable of people regarding this are the wives of the Messenger of Allah, peace and blessings of Allah be upon him." So he sent to Hafsah, and she said: "I have no knowledge of it." Then he sent to ‘Aishah, and she said: "If the circumcision passes the circumcision, ghusl becomes obligatory." He said: Umar became enraged—meaning he became angry—then he said: "Let it not reach me that anyone has done it and does not perform ghusl, or I will punish him severely."