SURAH AL-BAQARAH: 37

فَتَلَقَّىٰٓ ءَادَمُ مِن رَّبِّهِۦ كَلِمَـٰتٍ۬ فَتَابَ عَلَيۡهِ‌ۚ إِنَّهُ ۥ هُوَ ٱلتَّوَّابُ ٱلرَّحِيمُ

"THEN ADAM LEARNT CERTAIN WORDS (TO PRAY WITH) FROM HIS LORD; SO ALLAH ACCEPTED HIS REPENTANCE. NO DOUBT HE IS THE MOST-RELENTING, THE VERY MERCIFUL."

Part 1

There are are several different narrations from different Companions (Sahaba) about what those words were which were taught to Hazrat Adam AS for repentance. The generally accepted report is that of blessed Companion Sayyidna Ibn Abbas Razi Allah Anhu according to which these phrases are just the ones which the Holy Quran cites at another point;

رَبَّنَا ظَلَمۡنَآ أَنفُسَنَا وَإِن لَّمۡ تَغۡفِرۡ لَنَا وَتَرۡحَمۡنَا لَنَكُونَنَّ مِنَ ٱلۡخَـٰسِرِينَ (۷:۲۳)

"OUR LORD, WE HAVE WRONGED OURSELVES, AND IF YOU DO NOT FORGIVE US AND HAVE MERCY UPON US, WE WILL SURELY BE AMONG THE LOSERS." (7:23)

From Ma'ariful Quran, by Mufti Muhammad Shafi RE