What is the ruling and expiation for a person who fathered an illegitimate child with a married woman, then tried to abort it with injections that were unsuccessful, and then the child died three days after its birth under mysterious circumstances?

Adultery is one of the gravest major sins. It combines three aspects of reprehensibility: legal (Shar'i), rational ('Aqli), and customary ('Adi), as stated in the verse: "And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way." Its ugliness intensifies when committed with a married woman, as it involves an assault on a Muslim's honor and an attempt to abort the resulting pregnancy. The servant must offer sincere repentance, characterized by remorse, a firm resolve not to return to the sin, and an abandonment of everything that leads to this act. There is no specific expiation required as long as the fetus has not been aborted.