Musnad Ahmad 1153:2151

Asbat ibn Muhammad narrated to us, he said: Mutarrif narrated to us, from al-Sha'bi, from Masruq, from Aisha, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) would spend the night in a state of janabah (major ritual impurity), then Bilal would come to him and inform him of the prayer. He would then rise and perform ghusl (ritual bath), and I would look at the water dripping from his hair and his skin. Then he would go out, and I would hear his voice in the dawn prayer, and he would remain fasting."