(26) باب اسْتِحْبَابِ الذِّكْرِ بَعْدَ الصَّلاَةِ وَبَيَان صِفَتِهِ
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
If anyone extols Allah after every prayer thirty-three times, and praises Allah thirty-three times, and declares His Greatness thirty-three times, ninety-nine times in all, and says to complete a hundred:" There is no god but Allah, having no partner with Him, to Him belongs sovereignty and to Him is praise due, and He is Potent over everything," his sins will be forgiven even If these are as abundant as the foam of the sea.
Reference: Sahih Muslim 597 a
In-book reference: Book 5, Hadith 188
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1243