Riyad as-Salihin, Book 16, Hadith 1419 (In-Book) ⓘ

Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah said, "He who recites after every prayer: Subhan-Allah (Allah is free from imperfection) thirty-three times; Al-hamdu lillah (praise be to Allah) thirty-three times; Allahu Akbar (Allah is Greatest) thirty-three times; and completes the hundred with: La ilaha illallahu, wahdahu la sharika lahu, lahul-mulku wa lahul-hamdu, wa Huwa 'ala kulli shai'in Qadir (there is no true god except Allah. He is One and He has no partner with Him. His is the sovereignty and His is the praise, and He is Omnipotent), will have all his sins pardoned even if they may be as large as the foam on the surface of the sea."[Muslim].

وعنه عن رسول الله صلى الله عليه وسلم قال‏:‏ ‏"‏من سبح الله في دبر كل صلاة ثلاثًا وثلاثين، وحمد الله ثلاثًا وثلاثين، وكبر الله ثلاثًا وثلاثين، وقال تمام المائة‏:‏ لا إله إلا الله وحده لا شريك له، له الملك وله الحمد، وهو على كل شيء قدير، غفرت خطاياه وإن كانت مثل زبد البحر” ‏(‏‏(‏رواه مسلم‏)‏‏)‏