سُبْحـانَكَ اللّهُـمَّ وَبِحَمدِك، أَشْهَـدُ أَنْ لا إِلهَ إِلاّ أَنْتَ أَسْتَغْفِرُكَ وَأَتوبُ إِلَـيْك
Subhānaka Allāhumma wa biḥamdik, ash-hadu an lā ilāha illā ant, astaghfiruka wa atību ilayk. 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. Reference: Abu Dawud, Ibn Majah, At-Tirmidhi and An-Nasa'i. See also Al-Albani, Sahih At-Tirmidhi 3/ 153. 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 ... (then she quoted the above)." This was reported by An-Nasa'i in 'Amalul-Yawm wal-Laylah (no.308), and Dr. Farooq Hamadah graded it authentic in his checking of the same book, p. 273. See also Ahmad 6/77
Reference : Hisn al-Muslim 196