رَبِّ اغْفِرْ لِي، وَتُبْ عَلَيَّ، إِنَّكَ أَنْتَ التَّوَّابُ الغَفُوْرُ.
Ibn Umar (ra) said: It would be counted that the Messenger of Allah r would say one hundred times at any one sitting before getting up:
‘O my Lord, forgive me and turn towards me (to accept my repentance). Verily You are The Oft-Returning. The Oft-Forgiving.’
Source: Hisnul Muslim