What is the ruling on adultery (zina) in Islam, and is the prescribed punishment (hadd) applied to someone who seeks forgiveness and repents during the act of intercourse without completing it?

Adultery is one of the gravest sins, and the sin of a married person is even more severe. However, Allah accepts repentance; in fact, He rejoices in it and transforms bad deeds into good ones. One who repents from a sin is like one who has committed no sin. Repentance involves abandoning the sin, regretting it, and resolving not to return to it, while concealing oneself and not publicizing it. The implementation of religious penalties is entrusted to the ruler. A Muslim should conceal himself and strive in repentance if the matter has not reached the ruler.