Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said to him: "O boy! Shall I not give you something? Shall I not give you a present? Shall I not give you a gift?" I said: "Yes, O Messenger of Allah! May my father and mother be sacrificed for you." The narrator says: I thought that perhaps the Prophet (peace and blessings be upon him) would give me some wealth. He said: "Four rak'ahs which you should pray every day. If you are not able to do that, then pray them once a week; if you are not able to do that either, then pray them once a month; if you are not able to do that either, then pray them once a year; and if you are not able to do that either, then pray them once at some point in your life. You say the takbir and recite Surah al-Fatihah and a surah once, then you say 'Subhan Allah, wal-hamdu lillah, wa la ilaha illallah, wallahu akbar' (Glory be to Allah, all praise is for Allah, there is no god but Allah, and Allah is the Greatest) fifteen times. Then in bowing you say these words ten times; then when you rise, you say these words ten times; then when you go into prostration, you say these words ten times; then when you rise, you say these words ten times. Then you do the same throughout your prayer. When you have finished, after the tashahhud and before saying the salam, recite: 'O Allah! I ask You for the enabling grace of the people of guidance, the deeds of the people of certainty, the sincerity of those who repent, the resolve of those who are patient, the striving of those who fear, the seeking of those who long, the devotion of the God-fearing, and the insight of the people of knowledge, so that I may keep fearing You. O Allah! I ask You for such fear as will hold me back from disobeying You, so that I may do such acts of obedience to You by which I become deserving of Your pleasure, and so that I may turn to You in sincere repentance out of fear of You, and make my sincerity purely for You out of love for You, and so that I may rely on You in all affairs, having a good opinion of You. Glory be to You, O Creator of the Fire!'" (After this the Prophet (peace and blessings be upon him) said:) "O Ibn Abbas! When you do this, Allah Almighty will forgive all your sins, small and great, old and new, secret and open, deliberate and mistaken."
Al-Tabarani recorded it in al-Mu'jam al-Awsat.