Genesis 18:21 (KJV)

And the men rose up from thence, and looked toward Sodom: and Abraham went with them to bring them on the way.

And the LORD said, Shall I hide from Abraham that thing which I do;

Seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him?

For I know him, that he will command his children and his household after him, and they shall keep the way of the LORD, to do justice and judgment; that the LORD may bring upon Abraham that which he hath spoken of him.

And the LORD said, Because the cry of Sodom and Gomorrah is great, and because their sin is very grievous;

And the men turned their faces from thence, and went toward Sodom: but Abraham stood yet before the LORD.

And Abraham drew near, and said, Wilt thou also destroy the righteous with the wicked?

Peradventure there be fifty righteous within the city: wilt thou also destroy and not spare the place for the fifty righteous that are therein?

That be far from thee to do after this manner, to slay the righteous with the wicked: and that the righteous should be as the wicked, that be far from thee: Shall not the Judge of all the earth do right?

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