كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5
The Book of Mosques and Places of Prayer
(26)
Chapter: It is recommended to recite statements of remembrance after the prayer, and how that is to be done
(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.
حَدَّثَنِي عَبْدُ الْحَمِيدِ بْنُ بَيَانٍ الْوَاسِطِيُّ، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنْ سُهَيْلٍ، عَنْ أَبِي عُبَيْدٍ الْمَذْحِجِيِّ، - قَالَ مُسْلِمٌ أَبُو عُبَيْدٍ مَوْلَى سُلَيْمَانَ بْنِ عَبْدِ الْمَلِكِ - عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، عَنْ أَبِي هُرَيْرَةَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم ‏ "‏ مَنْ سَبَّحَ اللَّهَ فِي دُبُرِ كُلِّ صَلاَةٍ ثَلاَثًا وَثَلاَثِينَ وَحَمِدَ اللَّهَ ثَلاَثًا وَثَلاَثِينَ وَكَبَّرَ اللَّهَ ثَلاَثًا وَثَلاَثِينَ فَتِلْكَ تِسْعَةٌ وَتِسْعُونَ وَقَالَ تَمَامَ الْمِائَةِ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَىْءٍ قَدِيرٌ غُفِرَتْ خَطَايَاهُ وَإِنْ كَانَتْ مِثْلَ زَبَدِ الْبَحْرِ ‏"‏ ‏.‏
Reference : Sahih Muslim 597 a
In-book reference : Book 5, Hadith 188
USC-MSA web (English) reference : Book 4, Hadith 1243
  (deprecated numbering scheme)