Musnad Ahmad 1153:1350

Hashim narrated to us, from Sayyar, from al-Sha'bi, from Aisha, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) would come to the basin and perform ghusl (full ablution) from it due to janabah (major ritual impurity) after he had entered the morning, then he would remain fasting for that day."