Aishah (RA) said: 'Allah's Messenger (sal-Allaahu 'alayhe wa sallam) did not sit in a gathering, and did not recite the Qur'an, and did not perform any prayer without concluding by saying:

سُبْحَانَكَ اللّٰهُمَّ وَبِحَمْدِكَ، أَشْهَدُ أَنْ لَا إِلٰهَ إِلَّا أَنْتَ، أَسْتَغْفِرُكَ وَأَتُوْبُ إِلَيْكَ

Glory is to You, O Allah, and praise is to You. I bear witness that there is none worthy of worship but You. I seek Your forgiveness and repent to You.

Subhaanaka Allaahumma wa bihamdika, 'ash-hadu 'an laa 'ilaaha 'illaa 'Anta, 'astaghfiruka wa 'atoobu 'ilayka.