Musnad Ahmad 1153:1884

Abu Kamil narrated to us, he said: Hammad narrated to us, from Thabit al-Bunani, from Abdullah ibn Rabah, from Abd al-Aziz ibn al-Nu'man, from Aisha, who said: The Prophet, peace and blessings of Allah be upon him, said: "When the two circumcised parts meet, he must perform ghusl (ritual bath)."