עֶרְוַת בַּת בִּנְךָ אוֹ בַת בִּתְּךָ לֹא תְגַלֶּה עֶרְוָתָן כִּי עֶרְוָתְךָ הֵנָּה
The nakedness of your son's daughter or of your daughter's daughter, their nakedness you may not uncover for theirs is your own nakedness.
This verse is the prohibition against incest with a granddaughter. The prohibition against incest with a daughter appears… nowhere! Obviously, it’s prohibited, but where is the textual source? The Talmud in Yevamos (3a) derives the prohibition from a gezeira shava (comparison of identical terms) between our verse and the prohibition against a man having relations (separately) with both a woman and her daughter (verse 17). Incest with a daughter is one of the 613 mitzvos – and a capital crime – yet there’s nothing explicit about it in the Written Torah!