אַל־תִּפְנ֤וּ אֶל־הָאֹבֹת֙ וְאֶל־הַיִּדְּעֹנִ֔ים אַל־תְּבַקְשׁ֖וּ לְטָמְאָ֣ה בָהֶ֑ם אֲנִ֖י יְהוָ֥ה אֱלֹהֵיכֶֽם׃
Turn ye not unto the ghosts, nor unto familiar spirits; seek them not out, to be defiled by them: I am the LORD your God.
Read kabbalistic (mystical) interpretation of Leviticus 19:31: and classical mystical sources.