Musnad Ahmad 1156:81

Abu al-Nadr narrated to us, Sharik narrated to us, from Muhammad ibn Abd al-Rahman, the freed slave of the family of Talhah, from Kurayb, from Umm Salamah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) would be in a state of major ritual impurity (janabah), then he would sleep, then he would wake up, then he would sleep."