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