Zohar
He [Rabbi Aba] answered: regarding the ways of your Master and the decrees of your Master, why would you worry? About what you have the permission to know and see, ask; about what you do not have permission to know it is written "do not let your mouth make your flesh sin" (Eccl. 5:5), since the ways and secrets of the Holy Blessed One, God's higher secrets, are closed and hidden, and we do not have permission to ask. He [Rabbi Yehuda] replied: If so, all of Torah is closed and hidden, since it is a Name of the Holy One, and one who studies Torah is like one who studies the Holy Name, and if so, we have no permission to ask or see [anything about Torah].
Zohar
Rabbi Hamnuna-Saba then said as follows: (Ecclesiastes 5:5) “Do not let your mouth cause your body to sin,” i.e., one must not allow his mouth to get close to evil and be the cause of sin for the sacred flesh, which bears the mark of the holy covenant with the Creator. If he does so, he shall be dragged to hell. And the ruler of hell, called Domeh, stands at the gates of hell with hundreds of thousands of angels, but he is forbidden to approach those who have kept the holy covenant in this world.
Zohar
Therefore, every person should be careful not to say what King David said, because he will not be able to say to Dumah, "it was an error" (Eccl. 5:5), as it was with David. Because in David's case, the Holy One, blessed be He, defeated (Dumah) in the case. "Wherefore should Elohim be angry at your voice" (Ibid.) refers to the voice that said, "and destroy the work of your hands" (Ibid.). This is the sacred flesh, the holy covenant that he damaged, and because of which he is to be dragged down to Gehenom by the angel Dumah.