Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"The Messenger of Allah (saw) said to Abbas bin Abdul-Muttalib: 'O Abbas, O my uncle, shall I not give you a gift, shall I not give you something, shall I not tell you of something which, if you do it, will expiate for ten types of sins? If you do them, Allah will forgive you your sins, the first and the last of them, the old and the new, the unintentional and the deliberate, the minor and the major, the secret and the open, ten types of sin. Pray four Rakah, and recite in each Rakah the Opening of the Book (Al-Fatihah) and a Surah. When you have finished reciting in the first Rakah, while you are standing, say: Subhan-Allah wal- hamdu Lillah wa la ilaha illallah wa Allahu Akbar (Glory if to Allah, praise is to Allah, none has the right to be worshipped but Allah and Allah is the Most Great) fifteen times. Then bow and say it ten times while you are bowing. Then raise your head from Ruku and say it ten times. Then go into prostration and say it ten times while you are prostrating. Then raise your head from prostration and say it ten times. Then prostrate and say it ten times. Then raise your head from prostration and say it ten times. That will be seventy-five times in each Rakah. Do that in all four Rakah. If you can pray it once each day then do so. If you cannot, then once each week; if you cannot, then once each month. If you cannot, then once in your lifetime.'" Sahih