וַתֹּ֧אמֶר הַבְּכִירָ֛ה אֶל־הַצְּעִירָ֖ה אָבִ֣ינוּ זָקֵ֑ן וְאִ֨ישׁ אֵ֤ין בָּאָ֙רֶץ֙ לָב֣וֹא עָלֵ֔ינוּ כְּדֶ֖רֶךְ כָּל־הָאָֽרֶץ׃
And the first-born said unto the younger: ‘Our father is old, and there is not a man in the earth to come in unto us after the manner of all the earth.
Read halakhic rulings (Jewish law) on Genesis 19:31: and classical halakhic sources.