Musnad Ahmad 1153:1491

'Ali ibn 'Asim narrated to us, from Khalid, from Abu Qilabah, from 'Abd al-Rahman ibn 'Attab, who said: Abu Hurayrah used to say: "Whoever wakes up in a state of major ritual impurity (junub), there is no fast for him." He said: So Marwan ibn al-Hakam sent me—along with another man—to 'Aishah and Umm Salamah to ask them about the person who is in a state of major ritual impurity and wakes up in Ramadan before performing ghusl. He said: One of them said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to wake up in a state of major ritual impurity, then he would perform ghusl and complete the fast of his day." He said: The other said: "He used to wake up in a state of major ritual impurity without having had a wet dream, then he would complete his fast." He said: So they returned and informed Marwan of that. He said to 'Abd al-Rahman: "Inform Abu Hurayrah of what they both said." Abu Hurayrah said: "That is what I used to think, and that is what I used to suppose." He said: Marwan said to him: "With 'I suppose' and 'I think' you issue fatwas to the people?"