Rashi on Genesis 18:28/רש"י על בראשית י״ח:כ״ח

1התשחית בחמשה WILT THOU DESTROY ON ACCOUNT OF THE FIVE — Will there not still be nine for each city, and You, the All-Righteous One of the Universe, can be counted with them to make up the original number of ten! (Genesis Rabbah 49:9).