Humaid says that someone asked Hazrat Anas (may Allah be pleased with him) about the voluntary fasts of the Prophet (peace and blessings be upon him), so he replied that the Prophet (peace and blessings be upon him) would sometimes fast continuously in a month to the extent that we would think that now the Prophet (peace and blessings be upon him) will not leave any fast, and sometimes he would leave fasting to the extent that we would say that perhaps now the Prophet (peace and blessings be upon him) will not fast at all.