Rabbi Jehudah said: Rebecca was barren for twenty years. After twenty years (Isaac) took Rebecca and went (with her) to Mount Moriah, to the place where he had been bound, and he prayed on her behalf concerning the conception of the womb; and the Holy One, blessed be He, was entreated of him, as it is said, "And Isaac intreated the Lord" (ibid. xxv. 21). The children were contending with one another within her womb like mighty warriors, as it is said, "And the children struggled together within her" (ibid. 22).
The time of her confinement came round, and her soul was nigh unto death owing to her pains. And she went to pray in the place whither she and Isaac had gone, as it is said, "And she went to inquire of the Lord" (ibid.). What did the Holy One, blessed be He, do? Jacob took hold of the heels of Esau to make him fall, as it is said, "And after that came forth his brother, and his hand had hold on Esau's heel" (ibid. 26).
Hence thou mayest learn that the descendants of Esau will not fall until a remnant || from Jacob will come and cut off the feet of the children of Esau from the mountain of Seir, as it is said, "Forasmuch as thou sawest that a stone was cut out of the mountain without hands" (Dan. 2:45). Another Scripture text says, "Vengeance is mine, and a recompence, at the time when their foot shall slide" (Deut. 32:35).