זוהר בראשית — דף קכז ע”א

The Zohar asks why one who observes the chirping of birds is called a “serpent,” and answers that an impure spirit rests on the bird, and that the serpent will be removed from the world in the future. Rabbi Yehuda explains that Abraham knew a sign in the cave, where his heart and will were set, because he had entered it earlier and seen Adam and Eve buried there; a gate of the Garden of Eden had opened for him. Anyone who looks at the image of Adam does not escape death, but Abraham saw it and survived; he also saw the light shining in the cave and a lamp burning. Therefore, when he sought a burial place for Sarah, he acted wisely: he did not ask for the cave at once but for a burial holding among the sons of Heth, so as not to reveal his desire.