Humaid At-Tawil narrates: It was asked from Sayyiduna Anas (may Allah be pleased with him) about the voluntary fasting of the Prophet (peace and blessings be upon him): He replied: The Prophet (peace and blessings be upon him) would begin to observe voluntary fasts in a month to such an extent that we would think he would not leave any day of that month without fasting, and sometimes he would not observe any voluntary fast in a month to such an extent that we would think he would not fast at all in that month. If you wished to see the Prophet (peace and blessings be upon him) praying at night, you could see him praying, and if you wished to see him sleeping, you could see him sleeping as well.