Kabbalah su Genesi 18:29

Rabbi Yosi said that the words "In this generation" are a tribute to Noah, who lived in such a wicked generation and nevertheless remained a righteous man and perfect. Even in the generation of Moses (Noah would have been considered righteous). But he was not able to protect the world, because there were not even ten (righteous people) in it. This was the case as described (regarding S'dom): "perhaps ten shall be found there" (Gen. 18:32). As not even ten were found, (S'dom was destroyed). The same happened here. Ten (righteous) people were not to be found; only Noah, his three sons and their wives. And they did not add up to ten.