Another interpretation: "And the two daughters of Lot conceived by their father" (Genesis 19:36) - the matter came from their father. See what is written: "and he did not know when she lay down and when she arose," and over [the word] there is a dot. Why? Because he was drunk from the evening before, but during the night his wine wore off and he sensed her. For this reason he is publicized [in disgrace] every Sabbath - behold, he made himself liable.
Lot Sobered by Night and Knew What He Did
Yalkut Shimoni on Torah 86:6
דָּבָר אַחֵר, וַתַּהֲרֶיןָ שְׁתֵּי בְנוֹת לוֹט מֵאֲבִיהֶן, מֵאֲבִיהֶן הָיָה הַדָּבָר רְאֵה מַה כְּתִיב וְלֹא יָדַע בְּשָׁכְבָהּ וּבְקוּמָה נָקוּד לָמָה שֶׁהָיָה שִׁכּוֹר מֵאֶמֶשׁ, אֲבָל בַּלַּיְלָה פָּג יֵינוֹ וְהִרְגִּישׁ בָּה. מִפְּנֵי כָּךְ הוּא מִתְפַּרְסֵם בְּכָל שַׁבָּת הֲרֵי הוּא חִיֵּב לְעַצְמוֹ.