Leviticus 19:19-20

19‘You are to keep My statutes. You shall not breed together two kinds of your cattle; you shall not sow your field with two kinds of seed, nor wear clothing of two kinds of material mixed together.

20‘Now if a man has intimate relations with a woman who is a slave acquired for [marriage to] another man, but who has not been redeemed nor given her freedom, there shall be punishment [after an investigation]; they shall not be put to death, because she was not free;