לֹא־יִקַּ֥ח אִ֖ישׁ אֶת־אֵ֣שֶׁת אָבִ֑יו וְלֹ֥א יְגַלֶּ֖ה כְּנַ֥ף אָבִֽיו׃ (ס)
Mishneh Torah, Negative Mitzvot
That a eunuch shall not marry a daughter of Israel, as it is said, “He that is crushed (or maimed in his privy parts) shall not enter into the congregation of the Lord” (Deut. 23:2; authorized English version 23:1).
Sefer HaChinukh
That a eunuch not marry a daughter of Israel: That one whose sexual organs were damaged by the blow of a person or an animal or a tree — meaning to say, not at the hands of the Heavens — to the point that he cannot reproduce is prevented from marrying a daughter of Israel. And about this is it stated (Deuteronomy 23:1), “No one whose testes are crushed or whose member is cut off shall come into the congregation of the Lord.”