It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that when the takbir was said in the morning (Fajr) prayer, the Prophet (peace and blessings be upon him) gestured to the Companions and went away himself. Then he (peace and blessings be upon him) came out of his house with drops of water falling from his (peace and blessings be upon him) head. He (peace and blessings be upon him) led them in prayer and then said: "I am only a human being; I was in a state of major ritual impurity (janabah), but I had forgotten."
Only al-Hasan bin Abd al-Rahman al-Harithi narrated it (in this way). Isma'il Ibn Ulayyah and others narrated it from Ibn Awn, from Muhammad (bin Sirin), from the Prophet (peace and blessings be upon him) as mursal, and that is the preserved (mahfuz) version; all of this is supporting evidence for the hadith of Abu Bakrah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4067