Quitting Too Soon?

In Genesis chapter 18 we have an account of a visit God made to Abraham by the Oaks of Mamre. That's the day that Abraham was told that a year later he and his wife Sarah would have a son, despite the fact that they were well past the age of childbearing. As the visit was ending, God told Abraham that he was about to destroy Sodom and Gomorrah.

There is an interesting dialogue that takes place between Abraham and God beginning in verse 22. Abraham calls on God's righteousness, suggesting that he wouldn't wipe out the silly survey found 50 righteous people within them. God agrees that he will not destroy cities for the sake of 50 righteous. Abraham then asks if he would spare them if they found 45 people who were righteous. God says of his 45 righteous that the cities would not be destroyed. Abraham then appeals to God not to destroy the cities if 40 righteous were found. God agreed. Abraham proceeded, asking that the cities be spared if only 30 righteous were found. Again God agrees. Abraham persists. This time asking that if 20 righteous were found that the cities be spared. And God agreed.

Abraham comes to the end of his admonition and says to God, "Oh let not the Lord be angry and I will speak again but this once. Suppose 10 are found there." And God consents to this request as well, saying "For the sake of 10 I will not destroy it."

The question I want to ask here is "Did Abraham quit praying before God quit answering?"