It wasnarrated from Hudhaifah that the Prophet (ﷺ) used to saybetweenthe two prostrations:
"Rabbighfir li, Rabbighfir li (O Lordforgiveme, O Lord forgive me)." (IT)
English reference (IT): Vol. 1, Book 5, Hadith 897 (IT)
Arabic reference (IT): Book 5, Hadith 947 (IT)