Prophet Adam - The First Four Children

The pinnacle of earthly bliss was reached when Adam and Eve witnessed the birth of their first children, a set of twins. Adam was a devoted father and Eve a contented mother. The twins were Cain (Qabil) and his sister. Later Eve gave birth to a second set of twins, Abel (Habil) and his sister. The family enjoyed the bounties and fruits of the earth provided by their Lord. The children grew up to be strong and healthy young adults. Cain tilled the land, while Abel raised cattle.

Cain's Disobedience
The time arrived when the two young men desired life partners. This was part of Allah's plan for mankind, to multiply and form nations with different cultures and colors. Allah revealed to Adam that he should marry each son to the twin sister of the other. Adam instructed his children according to Allah's command, but Cain was displeased with the partner chosen for him, for Abel's twin-sister was not as beautiful as his own.

Cain's Jealousy of Abel
Adam was in a dilemma. He wanted peace and harmony in his family, so he invoked Allah for help. Allah commanded that each son offer a sacrifice, and he whose offering was accepted would have right on his side. Abel offered his best camel, while Cain offered his worst grain. His sacrifice was not accepted by Allah because of his disobedience to his father and the insincerity in his offering.
This enraged Cain even further. Realizing that his hopes of marrying his own beautiful sister were fading, he threatened his brother: "I will kill you! I refuse to see you happy while I remain unhappy!"
Abel, feeling sorry for his brother, replied: "It would be more proper for you, my brother, to search for the cause of your unhappiness and then walk in the way of peace. Allah accepts deeds only from those who serve and fear Him, not from those who reject His commands."