זוהר בראשית — דף קלח ע”א

The Zohar continues its description of the sons: according to the text, Esau was drawn after the serpent, and Jacob therefore dealt with him with cunning and wisdom in order to separate him, as it is said, “in the womb he took his brother by the heel” and “his hand held Esau’s heel.” The name “Jacob” was given to him by the Holy One, blessed be He, who saw that the primordial serpent is clever at evil and that a wise one should stand against it. Elsewhere the Holy One, blessed be He, calls Jacob “El”: “I am God above, and you are god below.” Rabbi Shimon explains “the great sea monsters” as Jacob and Esau, and Jacob became wise against him.