Genesis 18:31 (KJV)

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

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

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.

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.

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.

And he said, Oh let not the LORD be angry, and I will speak yet but this once: Peradventure ten shall be found there. And he said, I will not destroy it for ten's sake.

And the LORD went his way, as soon as he had left communing with Abraham: and Abraham returned unto his place.