זוהר בראשית — דף קכה ע”ב

The Zohar continues: a person who comes to purify himself is helped from above and is called holy, whereas one who comes to defile himself has bands of forces drawn to him and is called impure. Rabbi Yitzhak and Rabbi Yosi are walking from Tiberias to Lod, and Rabbi Yitzhak marvels at Balaam, all of whose deeds, according to the text, stemmed from the side of impurity. He explains that all kinds of serpents and sorcery are bound to the primordial serpent, and that a person draws down from above whatever side he arouses, holiness or impurity. Of Balaam it is said that he defiled himself every night with his donkey to draw an impure spirit upon himself, and then performed his sorcery. The text describes the start of his rites: he bound a serpent, split its head, and burned it all with herbs to make an incense.