Genesis 38:16

And he turned unto her by the way, and said, Go to, I pray thee, let me come in unto thee; (for he knew not that she was his daughter in law.) And she said, What wilt thou give me, that thou mayest come in unto me?

Cross-reference

Leviticus 18:15 explicitly forbids sex with a daughter-in-law — the law directly condemns what Judah unknowingly does here.

Ezekiel 16:33 portrays Israel as a prostitute who gives gifts to lovers — opposite to Tamar receiving payment from Judah.