Musnad Ahmad 1156:137

Yahya ibn Sa'id narrated to us, he said: Shu'bah narrated to us, Qatadah narrated to us, from Sa'id ibn al-Musayyib, from 'Amir, the brother of Umm Salamah, from Umm Salamah: "That the Prophet, peace and blessings of Allah be upon him, would wake up in a state of sexual impurity (junub), then he would perform ghusl and fast." He said: "Abu Hurairah rejected his (the Prophet's) fatwa."