اللَّهُمَّ أَنْتَ رَبِّي لا إِلَهَ إِلا أَنْتَ خَلَقْتَنِي وَأَنَا عَبْدُكَ
Allahumma anta Rabbi la ilaha illa anta, khalaqtani wa ana 'abduka...
O Allah, You are my Lord, there is no deity except You. You created me and I am Your servant...
Source: Sahih al-Bukhari
Known as Sayyidul Istighfar; recite morning and evening.