O Allah, You are my Lord. There is no god but You. You created me and I am Your — Repentance
اللَّهُمَّ أَنْتَ رَبِّي لَا إِلَهَ إِلَّا أَنْتَ خَلَقْتَنِي وَأَنَا عَبْدُكَ وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْتُ
Transliteration: Allaahumma anta rabbee laa ilaaha illaa anta khalaqtanee wa anaa 'abduk wa anaa 'alaa 'ahdika wa wa'dika mastata't
Translation: O Allah, You are my Lord. There is no god but You. You created me and I am Your servant, and I am upon Your covenant and promise as much as I can. (Sayyid al-Istighfar — opening)
Reference: Bukhari 7:150