Ikrimah narrates from Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said to Abbas (may Allah be pleased with him): "O Abbas! O uncle! Shall I not give you? Shall I not tell you ten qualities? When you do this, Allah will forgive all your sins: the first and the last, the new and the old, those committed deliberately and those by mistake, the open and the hidden. Those ten things are that you offer four rak'ahs and begin with the takbir; then recite Surah al-Fatihah and another surah; then, after finishing the surah, while standing, say 'Subhan Allah, wal-hamdu lillah, wa la ilaha illa Allah, wa Allahu akbar' (Glory be to Allah, all praise is for Allah, there is no god but Allah, and Allah is the Greatest) fifteen times; then bow and say it ten times while bowing; then raise your head from bowing and say it ten times while standing; then prostrate and say it ten times while in prostration; then raise your head from prostration and say it ten times; then say it ten times in prostration; then raise your head from prostration and say it ten times. That makes 75 times in every rak'ah. If you are able to pray it every day, do so; if you are not able, then every week; if you are not able even to do that, then once a month; if you are not able, then once a year; and if you are not able even to do that, then at least pray it once in your lifetime."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4916