Abu Bakr bin Abdur Rahman says that Hazrat Abu Hurairah (may Allah be pleased with him) used to say that if a person is in a state of major ritual impurity (junub) in the morning, his fast is not valid. Once I went to Hazrat Aisha (may Allah be pleased with her) and asked her opinion about this. She replied, "I cannot say anything about this. Sometimes the muezzin would give the call to prayer and I would see water flowing between the shoulders of the Prophet (peace and blessings be upon him), then the Prophet (peace and blessings be upon him) would perform the Fajr prayer and would fast on that day."