Musnad Abu Ya'la al-Mawsili 246:7

Abu Khaythama narrated to us, Waki' narrated to us, from Sufyan, from Abu Ishaq, from Sulayman ibn Surad, from Jubayr ibn Mut'im, who said: We discussed the ritual bath (ghusl) due to sexual impurity (janaba) in the presence of the Prophet, may Allah bless him and grant him peace. He said: "As for me, I pour three handfuls of water over my head."