It wasnarrated that Abu Rafi' said:
"The Messenger of Allah (ﷺ)saidto 'Abbas: 'O uncle, shall I not give you a gift, shall I notbenefit you, shall I not uphold my ties of kinship with you?' Hesaid:'Of course, O Messenger of Allah.' He said: 'Pray fourRak'ah, andrecite in each Rak'ah the Opening of the Book(Al-Fatihah) and aSurah. When you have finished reciting, say:Subhan-Allah wal-hamduLillah wa la ilaha illallah wa Allahu Akbar(Glory is to Allah, praiseis to Allah, none has the right to beworshipped but Allah and Allahis the Most Great) fifteen timesbefore you bow in Ruku'. Then bow andsay it ten times; then raiseyour head and say it ten times; thenprostrate and say it ten times;then raise your head and say it tentimes; then prostrate and say itten times; then raise your head andsay it ten times before you standup. That wil be seventy-five timesin each Rak'ah and three hundredtimes in the four Rak'ah, and even ifyour sins are like the grainsof sand, Allah will forgive you forthem.' He said: 'O Messengerof Allah, what if someone cannot say itin one day?' He said: 'Thensay it once in a week; if you cannot, thensay it once in a month'until he said: 'Once in a year.'"
English reference: Vol. 1, Book 5, Hadith 1386
Arabic reference: Book 5, Hadith 1449