Genesis 18:26

I will spare. God accepted the stipulation proposed by Abraham, not as an act of justice, but as an exercise of mercy. Justice required the preservation of the righteous, but mercy alone could spare the wicked. Presumably, also, the presence of a group of 50 righteous persons would offer hope for the conversion of others. God entered into Abraham’s reasoning and showed Himself willing to grant mercy to those who did not deserve it, for the sake of “fifty righteous.”