Musnad Ahmad 1153:2121

'Abd al-Samad narrated to us, he said: al-Muthanna, meaning Ibn Sa'id, narrated to us, he said: Qatadah narrated to us, from 'Urwah ibn al-Zubayr, from 'Aishah: "That the Messenger of Allah (peace and blessings of Allah be upon him), when he wanted to perform ghusl (ritual bath) from janabah (major ritual impurity), he would perform wudu (ablution) for prayer. Then he would pour [water] over his head three times, and he would penetrate the roots of the hair with his fingers."