Reference : Hisn al-Muslim 48

رَبِّ اغْفِـرْ لي ، رَبِّ اغْفِـرْ لي
Rabbi’ghfir lī, Rabbi’ghfir lī.

Lord, forgive me. My Lord, forgive me.

Reference:
Abu Dawud 1/231. See also Al-Albani, Sahihibn Mdjah 1/148.

Chapter: Between the two prostrations