It was narrated from Hudhaifah that the Prophet (ﷺ) used to say between the two prostrations:“Rabbighfir li, Rabbighfir li (O Lord forgive me, O Lord forgive me).”
Hadith No. 897
Sunan Ibn Majah
Gradings:
Al-Albani:
Sahih
Muhammad Fouad Abd al-Baqi:
Sahih
Shuaib Al Arnaut:
Sahih
Zubair Ali Zai:
Sahih Muslim