Sanhedrin 65
http://www.shemayisrael.co.il/dafyomi2/ ... ra-065.htm
Any man or woman who is involved in the practices of mediums or oracles shall be put to death ... (Leviticus 20:27)
This verse discusses the punishment for alien practices which were known as ov "mediums" and yid'oni, "oracles," which involved communication with the dead. This is the third instance in which this prohibition is reiterated.
We cannot help but link this last reference with the instructions to the kohanim in such a closely related matter.
The prohibition against the practices of ov and yid'oni are repeated yet again in the Book of Deuteronomy:
When you come to the land that the Lord your God has given you, do not learn to do the revolting practices of those nations ... nor practice Ov or Yid'oni or attempt to communicate with the dead. (Deut. 18:9-11).
From the context, we learn that ov and yid'oni were types of witchcraft involving communication with the dead. The Talmud (Sanhedrin 65b) explains that a human skull was used in the rite of ov.
http://www.aish.com/torahportion/moray/ ... ocence.asp