According to the laws of the Torah, one may not raise the spirits of the dead to talk to them. One who raises the spirits of the dead is called an ov. One who does raise the spirits of the dead must be stoned to death, for it is written “A man or a woman who is a medium, or who has familiar spirits, shall surely be put to death; they shall stone them with stones. Their blood shall be upon them” (Leviticus 20:27).
The early sages described how the medium operates: The dead speaks from the medium’s armpit or from his joints. The scholars asked: From the words of the prophet Isaiah it would appear that the dead speaks from its grave and not from the medium’s armpit, and that is why the spirit’s voice is weak. It is written “You shall be brought down, you shall speak out of the ground; your speech shall be low, out of the dust. Your voice shall be like a medium’s, out of the ground” (Isaiah 29:4). Because it says “Your voice shall be like a medium’s, out of the ground” it seems that the dead spirit which the medium raises speaks from the ground and its voice is weak. Answer: The prophet Isaiah meant that the spirit speaks from the medium’s armpit or from between his limbs. The scholars continued to ask: The medium who raised the spirit of the dead prophet Samuel, by request of King Saul, said “When the woman saw Samuel… And the woman said to Saul, ‘I saw a spirit ascending out of the earth'” (I Samuel 28:12-13). Because it says “ascending out of the earth” it means that Samuel spoke from the grave. Answer: Samuel sat between the medium’s limbs and spoke. The sages also clarified that there are two types of mediums: one raises the dead from its grave and sits it on the medium’s sexual organ, and one which speaks with the dead while the corpse’s skulls rests on the ground. What is the difference between these two types of mediums? Answer: If the dead is raised by a medium which will seat the spirit on its sexual organ, it does not rise up naturally. Its feet come first and then its head, and it cannot be raised on the Sabbath, only on a weekday. If the dead is raised by a medium which speaks to the spirit when its skull is on the ground, it will rise up naturally and not backwards, and it can be spoken to on the Sabbath. To support the claim that a medium which seats the spirit on his sexual organ cannot do so on the Sabbath, the scholars bring an incident involving the Roman governor [Tineius Rufus] and Rabbi Akiva. The governor asked Rabbi Akiva: How do you know that Saturday is the true Sabbath and that there was no mistake in the count of days, making Saturday a weekday? Rabbi Akiva answered him: There are several ways to check if Saturday is the true Sabbath. A medium cannot raise the dead and seat it on his sexual organ on the Sabbath; if he succeeds, the day was obviously not the Sabbath. The river Sabbation, in which rocks flow all week long, is quiet on the Sabbath, and the grave of the Roman governor’s father raised smoke all week long but not on the Sabbath, for purgatory stops on the Sabbath and the evil are given a day of rest.
(Babylonian Talmud, Tractate Sanhedrin 65b)