Rashi on Leviticus 20:10/רש"י על ויקרא כ׳:י׳

1ואיש AND THE MAN [THAT COMMITTETH ADULERY SHALL SURELY BE PUT TO DEATH] — a man, thus excluding a minor (Sifra, Kedoshim, Chapter 10 8).

2אשר ינאף את אשת איש WHO COMMITTETH ADULTERY WITH ANOTHER MAN'S WIFE — a man's wife, thus excluding the wife of a minor from the death penalty. This teaches us that a minor cannot enter into a marriage contract. And in reference to what married woman do I make you liable to the death penalty?

3אשר ינאף את אשת רעהו IF HE COMMITTETH ADULTERY WITH THE WIFE OF HIS FELLOW-MAN — his fellow-man, thus excluding the wife of a heathen; this teaches us that a heathen cannot enter into a marriage contract according to Jewish law (Sifra, Kedoshim, Chapter 10 8; Sanhedrin 52b).

4מות יומת הנאף והנאפת THE ADULTERER AND THE ADULTRESS SHALL SURELY BE PUT TO DEATH — Wherever a death penalty is mentioned in Scripture without being precisely defined, only strangulation is intended (Sifra, Kedoshim, Chapter 10 8; Sanhedrin 55b).