Midras Kejadian 24:51: Pirkei DeRabbi Eliezer & Bereshit Rabbah

Laban and Bethuel answered: Since (this) word has come forth from the mouth of the Almighty, we cannot prevent it, as it is said, "Then Laban and Bethuel answered and said, The thing proceedeth from the Lord: we cannot speak unto thee bad or good" (Gen. 24:50). "Behold, Rebecca is before thee; take her and go" (Gen. 24:51).

“Laban and Betuel answered and said: The matter has come forth from the Lord; we can speak to you neither bad nor good” (Genesis 24:50).
“Behold, Rebecca is before you, take her and go, and she will be a wife for your master’s son, as the Lord has spoken” (Genesis 24:51).
“Laban and Betuel answered and said: The matter has come forth from the Lord” – from where did it come forth? Rabbi Yehoshua bar Neḥemya in the name of Rabbi Ḥanina bar Yitzḥak: It came forth from Mount Moriah.³⁹It was immediately after Abraham’s binding of Isaac on Mount Moriah that Abraham was informed about Rebecca’s birth (Genesis 22:20–23). Her marriage to Isaac was foreordained from that point. The Rabbis say: From where did it come forth? “She will be a wife for your master’s son, as the Lord has spoken.”⁴⁰The marriage of Isaac and Rebecca was not foreordained upon her birth. The match between them was ordained in Heaven only now.