Volume 3, Book 31, Number 197:
Narrated ‘Abdullah bin ‘Amr:
Allah’s Apostle was informed that I had taken an oath to fast daily and to pray (every night) all the
night throughout my life (so Allah’s Apostle came to me and asked whether it was correct): I replied,
“Let my parents be sacrificed for you! I said so.” The Prophet said, “You can not do that. So, fast for
few days and give it up for few days, r ray and sleep. Fast three days a month as the reward of good
deeds is multiplied ten times and that will be equal to one year of fasting.” I replied, “I can do better
than that.” The Prophet said to me, “Fast one day and give up fasting for a day and that is the fasting
of Prophet David and that is the best fasting.” I said, “I have the power to fast better (more) than that.”
The Prophet said, “There is no better fasting than that.”