וַתַּשְׁקֶ֧יןָ אֶת־אֲבִיהֶ֛ן יַ֖יִן בַּלַּ֣יְלָה ה֑וּא וַתָּבֹ֤א הַבְּכִירָה֙ וַתִּשְׁכַּ֣ב אֶת־אָבִ֔יהָ וְלֹֽא־יָדַ֥ע בְּשִׁכְבָ֖הּ וּבְקׄוּמָֽהּ׃
And they made their father drink wine that night. And the first-born went in, and lay with her father; and he knew not when she lay down, nor when she arose.
Read kabbalistic (mystical) interpretation of Genesis 19:33: and classical mystical sources.