Genesis 18:28

²⁶  And the LORD said, If I find in Sodom fifty righteous within the city, then I will spare all the place for their sakes.

²⁷  And Abraham answered and said, Behold now, I have taken upon me to speak unto the LORD, which am but dust and ashes:

²⁸  Peradventure there shall lack five of the fifty righteous: wilt thou destroy all the city for lack of five? And he said, If I find there forty and five, I will not destroy it.

²⁹  And he spake unto him yet again, and said, Peradventure there shall be forty found there. And he said, I will not do it for forty's sake.

³⁰  And he said unto him, Oh let not the LORD be angry, and I will speak: Peradventure there shall thirty be found there. And he said, I will not do it, if I find thirty there.