14. How did Prophet Adam express remorse?

Verse 2:37 of the Quran says Adam (A.S) learnt a few words from the Creator, though the words are not mentioned in this verse, we find them in 7:23 as ’Our Lord we have brought injustice upon ourselves, if you do not show mercy, we are the ones who will turn out to be the losers. 

Both begged for mercy from God, and He forgave them if their sin is clear from this verse. Hence any one expressing remorse for sins committed without intent will be forgiven is evident from this verse.

Some cite a story that Adam sought mercy from God in the name Prophet Muhammad. 

The story goes on like this, when Adam (A.S.) was created he had a view of paradise with the words ‘There is no God except Allah, and Muhammad is the prophet of Allah’ inscribed on the gates to paradise. On seeing this Prophet Adam asked God about who Muhammad is and how his name is accompanying God Himself, to that God replied to Muhammad will be a descendent down the line and if it wasn't for Muhammad, He would not have created Adam himself. So, at the time of banishment from paradise Adam (A.S) remembered the inscriptions and pleaded for mercy in the name of Prophet Muhammad. This message can be found in the Hadith Books Tirmidi, and Haakim, as narrated by Abdur Rahman bin Zayd bin Aslam notorious for fabricating stories in the name of Hadiths. Hence this message is declared by scholars as fabricated.

The Quran clearly states in verse (7:33) the words used by Adam (A.S) in seeking forgiveness. But this message contradicting the Quran is a fabrication and more reason to disbelieve in these kinds of yarns against the Quran.

And moreover, to plead for forgiveness in the name of someone else with God Al-Mighty is meaningless.