זוהר בראשית — דף קפה ע”א

For one who engages in Torah for its own sake, the Torah walks before him when he leaves this world and protects him in the grave; “and when you awake, it will speak with you”: at the resurrection of the dead, the Torah he had abandoned will return and speak within him, in an even more perfected form. One who did not merit to engage in it is cast into Gehenna, and “the pit was empty” because there was no water in it. Israel was exiled from the land for having forsaken the Torah, and the world endures through the Torah. “They cast him into the pit” alludes to Egypt, a place where the secret of faith is absent. Rabbi Yitzhak asks about the snakes and scorpions in the pit, and answers that Reuben saw the danger in his brothers’ hands, since they hated him: it was better to fall into a pit of snakes than to be handed over to enemies.