Deuteronomy 4:10 - 4:20
... the day that thou stoodest before the Lord thy God in Horev, when the Lord said to me, Gather me the people together, and I will make them hear my words, that they may learn to fear me all the days that they shall live upon the earth, and that they may teach their children. And you came near and stood under the mountain; and the mountain burned with fire to the heart of heaven, with darkness , clouds, and thick darkness. And the Lord spoke to you out of the midst of the fire: you heard the voice of words, but saw no form; only a voice. ... Take therefore good heed to yourselves; for you saw no manner of form on the day that the Lord spoke to you in Horev out of the midst of the fire: lest you become corrupt, and make a carved idol, the similitude of any figure, the likeness of male or female, the likeness of any beast that is on the earth, the likeness of any winged bird that flies in the air, the likeness of any thing that creeps on the ground, the likeness of any fish that is in the waters beneath the earth; and lest thou lift up thy eyes to heaven, and when thou seest the sun, and the moon, and the stars, all the host of heaven, thou shouldst be misled to worship them, and serve them, which the Lord the God has allotted to all the nations under the whole heaven. But the Lord has taken you, and brought you out of the iron furnace, out of Mitzrayim, to be to him a people of inheritance, as you are this day.
Deuteronomy 13:2 - 13:5
If there arise among you a prophet, or a dreamer of dreams and he give thee a sign or a wonder, and the sign or the wonder come to pass, of which he spoke to thee, saying, Let us go after other gods, which thou has not known, and let us serve them; thou shalt not hearken to the words of that prophet, or that dreamer of dreams: for the Lord your God puts you to the proof, to know whether you love the Lord your God with all your heart and with all your soul..."