Mu'jam Kabir Tabarani 983 — the Messenger of Allah ﷺ said to Sayyiduna

It is narrated from Sayyiduna Abu Rafi' (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said to Sayyiduna al-Abbas (may Allah be pleased with him): "O uncle! Shall I not give you something, shall I not grant you a gift, shall I not benefit you?" He said: Certainly, O Messenger of Allah. He (peace and blessings be upon him) said: "Uncle! Pray four rak'ahs, and in each rak'ah recite Surah al-Fatihah and another surah. When the recitation is finished, say fifteen times before bowing: Allahu akbar, wal-hamdu lillah, wa subhan Allah, wa la ilaha illallah (Allah is the Greatest, all praise is for Allah, glory be to Allah, and there is no god but Allah). Then bow and say it ten times, then raise your head and say it ten times, then prostrate and say it ten times, then raise your head and say it ten times, then prostrate and say it ten times, then raise your head and say it ten times, then stand up. That makes seventy-five times in each rak'ah, and three hundred in four rak'ahs. Even if your sins were like the foam of the sea, Allah would forgive you." He said: O Messenger of Allah! Who is able to say it every day? He (peace and blessings be upon him) said: "If you cannot pray it daily, then pray it once a week" - until he said: "Pray it once a month" - until he said: "Pray it once a year."