Tafsiran Imamat 20:10: Rashi, Rashbam, Rabbeinu Bahya & Siftei Chakhamim

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

את אשת רעהו, excluding if he slept with a “wife” who was a gentile. The adulterer would then not face the death penalty.

ואיש אשר ינאף את אשת רעהו, “and the man who engages in an adulterous relationship with the wife of his fellow, etc.” our sages see in the word איש an exclusion of the death penalty for a minor between the ages of nine and thirteen who sleeps with the wife of a fellow Jew. In the words אשת רעהו they see an exclusion of the death penalty for someone who sleeps with the wife of a Gentile (compare Sanhedrin 52). The words אשת איש indicate that sleeping with the wife of a minor is also not subject to the death penalty. Our verse proves that a marriage ceremony entered into with a Gentile is not considered a legal marriage.

אשר 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?