al-Hasan bin Muhammad al-Za'farani الحسن بن محمد الصباح الزعفراني · The Book of Fasting

"The Messenger of Allah said: 'Whoever fasts for three days of each month, he has fasted for a whole lifetime.' Then he said: Allah has spoken the truth in His book: Whoever brings a good deed shall have ten times the like thereof to his credit.