Musnad Abu Ya'la al-Mawsili 159:111

Abu al-Rabi' narrated to us, Fulayh narrated to us, from Suhayl ibn Abi Salih, from 'Ata' ibn Yazid, who said: Abu Hurayrah said: The Messenger of Allah (ﷺ) said: "Whoever glorifies Allah (says SubhanAllah) thirty-three times, and magnifies Allah (says Allahu Akbar) thirty-three times, and praises Allah (says Alhamdulillah) thirty-three times, and says: 'There is no god but Allah alone, He has no partner, to Him belongs the dominion, and to Him belongs the praise, and He is capable of all things' (La ilaha illallah wahdahu la sharika lah, lahul-mulku wa lahul-hamdu wa huwa 'ala kulli shay'in qadir) after the prayer, his sin will be forgiven, even if it were more than the foam of the sea."