سُبْحَانَكَ اَللَّهُمَّ وَبِحَمْدِكَ، أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا أَنْتَ، أَسْتَغْفِرُكَ وَأَتُوبُ إِلَيْكَ

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

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. Aishah (RA) said: 'Allah's Messenger (ﷺ) did not sit in a gathering, and did not recite the Qur'an, and did not perform any prayer without concluding by saying: (The dua is mentioned above)

Reference: Hasan Sahih. Abu Dawud: 4859