Genesis 18:27 KJV
And Abraham answered and said, Behold now, I have taken upon me to speak unto the Lord, which am but dust and ashes:
Genesis 18:27, King James Version
In context
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.