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

1ואברהם היו יהיה SEEING THAT ABRAHAM SHALL SURELY BECOME — The Midrash applies to this the text Proverbs 10:7, “The mention of the righteous shall be for a blessing”: therefore, since He mentions him He blessed him (Genesis Rabbah 49:1). But its real meaning is: “Shall I conceal it from him, seeing that he is so beloved by Me as to become a great nation, and seeing that all nations of the earth shall bless themselves through him?”