Recite to them the truth of the story of the two sons of Adam. Behold! they each presented a sacrifice (to Allah): It was accepted from one, but not from the other. Said the latter: “Be sure I will slay thee.” “Surely,” said the former, “Allah doth accept of the sacrifice of those who are righteous.
The following excerpt is my personal opinion as I could not find a scholarly position to confirm it and no one is obliged to follow:
‘The scholars are divided as to who the two sons of Adam (peace be upon him) were. The traditionalists see them as the two sons of Adam, the first man. However all these excerpts originate from Jewish histories and are thus not authentic narrations Islamically. The other group of scholars take a metaphorical approach saying Ibn e Adam (Sons of Adam) is a metaphorical expression meaning two persons from the lineage of Adam or the early Hebrews.
*I categorically reject both opinions. Adam (peace be upon him) was the first prophet sent to Ibn e Adam, the children of Adam, or in other words, the human beings after the completion of their evolution on Earth. The story of Cain and Abel, in my opinion, is the story of the two sons of this historical Adam (peace be upon him) who was raised as the first prophet for humanity. The story of Cain and Abel is clouded with allegory so we cannot identify the exact portents of this narration; however, the general meaning can certainly be applied to this reference as a historical event.
To conclude, Adam (peace be upon him) was not the first man and neither a metaphorical human. He was with certainty the first prophet; and had two sons named Cain and Abel. The story of Cain and Abel is to be interpreted in this context.
For details on the prophethood of Adam, see the post: