Musnad Abu Ya'la al-Mawsili 129:74

Abu Sa'id al-Ashajj narrated to us, al-Muharibi narrated to us, from Salam ibn Sulaym, from Humayd, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The time for the woman experiencing postpartum bleeding is forty days, unless she sees purity before that."