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.

Wesley's Notes

18:30 Oh let not the Lord be angry - The importunity which believers use in their addresses to God is such, that if they were dealing with a man like themselves, they could not but fear that he would be angry with them. But he with whom we have to do is God and not man, and he is pleased when he is wrestled with. But why then did Abraham leave off asking when he had prevailed so far as to get the place spared if there were but ten righteous in it? Either, Because he owned that it deserved to perish if there were not so many: as the dresser of the vineyard, who consented that the barren tree should be cut down if one year's trial more did not make it fruitful, Luke 13:9. Or, Because God restrained his spirit from asking any farther. When God hath determined the ruin of a place, he forbids it to be prayed for, Jer 7:16.

Matthew Henry's Concise Commentary

18:23-33 Here is the first solemn prayer upon record in the Bible; and it is a prayer for the sparing of Sodom. Abraham prayed earnestly that Sodom might be spared, if but a few righteous persons should be found in it. Come and learn from Abraham what compassion we should feel for sinners, and how earnestly we should pray for them. We see here that the effectual, fervent prayer of a righteous man avails much. Abraham, indeed, failed in his request for the whole place, but Lot was miraculously delivered. Be encouraged then to expect, by earnest prayer, the blessing of God upon your families, your friends, your neighbourhood. To this end you must not only pray, but you must live like Abraham. He knew the Judge of all the earth would do right. He does not plead that the wicked may be spared for their own sake, or because it would be severe to destroy them, but for the sake of the righteous who might be found among them. And righteousness only can be made a plea before God. How then did Christ make intercession for transgressors? Not by blaming the Divine law, nor by alleging aught in extenuation or excuse of human guilt; but by pleading HIS OWN obedience unto death.