וַיֹּ֨סֶף ע֜וֹד לְדַבֵּ֤ר אֵלָיו֙ וַיֹּאמַ֔ר אוּלַ֛י יִמָּצְא֥וּן שָׁ֖ם אַרְבָּעִ֑ים וַיֹּ֙אמֶר֙ לֹ֣א אֶֽעֱשֶׂ֔ה בַּעֲב֖וּר הָאַרְבָּעִֽים׃
And he spoke unto Him yet again, and said: ‘Peradventure there shall be forty found there.’ And He said: ‘I will not do it for the forty’s sake.’
Read halakhic rulings (Jewish law) on Genesis 18:29: and classical halakhic sources.