Musnad Ahmad 32:2096

'Affan narrated to us, Hammad narrated to us, 'Ali ibn Zayd informed us, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) used to pass by the door of Fatimah for six months when he went out for the dawn prayer, saying: "Prayer, O people of the house! {Allah only intends to remove from you the impurity, O people of the [Prophet's] household, and to purify you with [extensive] purification} [Al-Ahzab: 33]."