Torah Portion: Yisro
Do not commit adultery (Shemos 20:13).
It is forbidden by a negative commandment to be conjugally intimate with a married woman, at it says: Do not commit adultery [tin’af] (Shemos 20:13). The term ni’uf (adultery) by itself connotes a married woman.
Among the roots of this commandment is the idea that the world should be settled as Hashem desired; and Hashem, blessed is He, willed that everything in His world should produce its fruit (offspring), each according to its species, and no one species should become intermingled with another. He also willed about human offspring that it be known whose child it is so that they should not become intermingled with one another. [Adultery] also leads to a number of other harmful results in that it causes the violation of several mitzvos which God placed on us.