Musnad Ahmad 1153:897

'Affan narrated to us, he said: Hammad ibn Salamah narrated to us, he said: Thabit narrated to us, from 'Abdullah ibn Rabah, from 'Abd al-'Aziz ibn al-Nu'man, from 'Aishah, she said: "When the two circumcised parts met, the Messenger of Allah, peace and blessings of Allah be upon him, would perform ghusl (ritual bath)."