Adam's sin in Islam was disobeying God's command by eating from the forbidden tree, also referred to as the Tree of Immortality.
According to Islamic teachings, God placed Adam (and his wife Hawwa/Eve) in Paradise and allowed them to enjoy all its blessings. However, God forbade them from approaching or eating from a specific tree. Satan tempted them, suggesting that eating from the tree would grant them immortality and a kingdom that would never decay. Adam and Hawwa yielded to this temptation and ate from the forbidden tree, thereby disobeying God's direct command.
The consequences of this act were significant. Adam and Hawwa became aware of their nakedness and were expelled from Paradise. This event is interpreted both literally and allegorically. Literally, it represents a specific act of disobedience. Allegorically, it symbolizes humanity's relationship with God, the potential for temptation, and the consequences of straying from divine guidance. The act of eating from the tree represents a deviation from God's will and a preference for worldly desires over divine commands. This led to their descent to Earth, marking the beginning of human life and the challenges associated with it.