Ibn Umar (ra) said: Allah's Messenger (ﷺ) used to repeat in a single sitting:
Rabbigh’fir lī
wa tub `alayy
innaka antat-Tawwābu ‘l-Ghafūr.
Ibn Umar (ra) said: Allah's Messenger (ﷺ) used to repeat in a single sitting:
My Lord, forgive me,
and accept my repentance,
You are the Ever-Relenting, the All-Forgiving.
Reference:
Sahih Ibn Majah 2/321. See also Al-Albani, Sahih At-Tirmidhi 3/153.