Sefer HaChinuch ספר החינוך

To not inquire of the dead: To not inquire of the dead. And the content of this inquiring (see Sefer HaMitzvot, Negative Commandments 38) is that there are people that starve themselves and lay down in the cemetery, so that the dead will come to them in a dream and inform that which they asked him about; and there are others who wear well-known clothes and say things and offer well-known incense and sleep alone so that the dead who they want will come and speak to them in a dream. And about all of these types of crafts and similar to them is it stated (Deuteronomy 18:10-11), “There shall not be found in you, etc. or one who inquires of the dead.”

What I wrote on the prohibition of magic in this Order (Sefer HaChinukh 511) and in the Order of Mishpatim (Sefer HaChinukh 62) is from the roots of the commandment.

And the laws of the commandment are in Sanhedrin (Chapter 7).

And this prohibition is practiced in every place and at all times by males and females. And one who transgresses it and does any act so that the dead will come and inform him anything is liable for lashes.