Musnad Ahmad 1153:376

Abu al-Mundhir Isma'il ibn 'Umar narrated to us, he said: Malik—meaning Ibn Anas—narrated to us, from 'Abdullah ibn 'Abd al-Rahman ibn Ma'mar, from Abu Yunus, the freed slave of 'A'ishah, from 'A'ishah, that a man asked the Messenger of Allah, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, the prayer overtakes me while I am in a state of major ritual impurity (junub), and I intend to fast?" The Messenger of Allah, peace and blessings of Allah be upon him, said: "And the prayer overtakes me while I am in a state of major ritual impurity, and I intend to fast, so I perform ghusl (ritual bath), then I fast." The man said: "We are not like you, for Allah has forgiven you your past sins and your future ones." The Messenger of Allah, peace and blessings of Allah be upon him, became angry and said: "By Allah, I truly hope that I am the most fearful of you toward Allah, the Mighty and Majestic, and the most knowledgeable of you regarding what I must guard against."