Leviticus 19:31 - Regard not them that have familiar spirits, neither seek after wizards, to be defiled by them: I am the LORD your God. Isaiah 8:19 - And when they shall say unto you, Seek unto them that have familiar spirits, and unto wizards that peep, and that mutter: should not a people seek unto their God? for the living to the dead? Isaiah 19:3 - And the spirit of Egypt shall fail in the midst thereof; and I will destroy the counsel thereof: and they shall seek to the idols, and to the charmers, and to them that have familiar spirits, and to the wizards. Leviticus 20:6 - And the soul that turneth after such as have familiar spirits, and after wizards, to go a whoring after them, I will even set my face against that soul, and will cut him off from among his people. 2 Chronicles 33:6 - And he caused his children to pass through the fire in the valley of the son of Hinnom: also he observed times, and used enchantments, and used witchcraft, and dealt with a familiar spirit, and with wizards: he wrought much evil in the sight of the LORD, to provoke him to anger. 2 Kings 23:24 - Moreover the workers with familiar spirits, and the wizards, and the images, and the idols, and all the abominations that were spied in the land of Judah and in Jerusalem, did Josiah put away, that he might perform the words of the law which were written in the book that Hilkiah the priest found in the house of the LORD. Leviticus 20:27 - A man also or woman that hath a familiar spirit, or that is a wizard, shall surely be put to death: they shall stone them with stones: their blood shall be upon them. 1 Samuel 28:3-25 - Now Samuel was dead, and all Israel had lamented him, and buried him in Ramah, even in his own city. And Saul had put away those that had familiar spirits, and the wizards, out of the land.
1 Chronicles 10:13 - So Saul died for his transgression which he committed against the LORD, even against the word of the LORD, which he kept not, and also for asking counsel of one that had a familiar spirit, to enquire of it; Deuteronomy 18:11 - Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer.
The Lesser Key of Solomon seems to take the idea of the familiar spirit very seriously. The text states that the demon Paimon gives good familiars "as such can teach all arts." Buer gives good familiars. Purson gives good familiars, so does Marax. Gaap can steal familiars out of the custody of other magicians. Malphas also gives good familiars. So does Sabnock. So does Shax "sometimes." Alloces "bringeth unto thee good familiars." Amy gives good familiars. Amdusias also gives good familiars. Belial "giveth excellent familiars."
And finally, the spirit Valefor may BE a familiar, though he might tempt you to steal. Here is his description in the Lesser Key of Solomon. (6.) VALEFOR.—The Sixth Spirit is Valefor. He is a mighty Duke, andappeareth in the shape of a Lion with an Ass’s Head, bellowing. He is agood Familiar, but tempteth them he is a familiar of to steal. He governeth 10 Legions of Spirits. His Seal is this, which is to be worn,whether thou wilt have him for a Familiar, or not.