Islamic Beliefs on the Soul
According to few verses from the Qur'an, the creation of humans involves Allah "breathing" souls into them. This intangible part of an individual's existence is "pure" at birth. It has the potential of growing and achieving nearness to God if the person leads a righteous life. At death, the person's soul transitions to an eternal afterlife of bliss, peace and unending spiritual growth until the day of judgement where both the body and soul are reunited for judgement at which point the person is either rewarded by going to heaven if they have followed God's commands or punished if they have disobeyed him.
From the Hadith we understand that Allah assigns an Angel to "breathe" soul into an embryo after 40 days of pregnancy.
Generally, it is believed that all living beings comprise two aspects during their existence: The physical (being the body) and the non-physical (being the soul). The non-physical aspect, namely the soul, is one's soul-related activities like his/her feelings and emotions, thoughts, conscious and sub-conscious desires and objectives. While the body and its physical actions serve as a "reflection" of one's soul, whether it was good or evil, and thus "confirms" the extent of such intentions. The soul enters heaven, not the body.