Sifrei Devarim 11

¹(Devarim 1:11) "May the L-rd, the G-d of your fathers, add to you, such as you, a thousand times!" They said to him: Our teacher, Moses, we do not want you to bless us. The Holy One Blessed be He promised Abraham our father (Bereshith 22:17) "… and multiply, will I multiply your seed as the stars of the heavens, and I will make your seed like the sand on the seashore" — and you set a limit to our blessing! He answered: This is my (blessing). An analogy: A king had many possessions and a young son, and he (the king) had to go abroad. He said: If I leave my possessions in the hand of my son, he will squander them. So saying, he appointed a caretaker (for his possessions) until his son would grow up and he (the caretaker) gave him (his son) enough of his own for his sustenance — whereupon the son cried: Is this all the silver and gold that my father has left me? And the caretaker: Everything I have given you is mine. What your father left for you is in keeping for you. Thus did Moses say to Israel: "May the L-rd, the G-d of your fathers, add to you, such as you, a thousand times." This is my (blessing to you). As far as yours is concerned, ( Ibid .)_ "and may He bless you as He spoke to you" — as the sand of the seas, and the dust of the earth, and as the fish of the ocean, and as the stars of the heavens, in abundance.