False Spirits

"And it came to pass that I saw a man, and he was dressed in a white robe; and he came and stood before me. And it came to pass that he spake unto me, and bade me follow him. And it came to pass that as I followed him [for many hours] I beheld myself that I was in a dark and dreary waste." (1 Nephi 8:5-7)

Mistaking false for true prophets

"But behold, if a man shall come among you and shall say: Do this, and there is no iniquity; do that and ye shall not suffer; yea, he will say: Walk after the pride of your own hearts; yea, walk after the pride of your eyes, and do whatsoever your heart desireth—and if a man shall come among you and say this, ye will receive him, and say that he is a prophet. Yea, ye will lift him up, and ye will give unto him of your substance; ye will give unto him of your gold, and of your silver, and ye will clothe him with costly apparel; and because he speaketh flattering words unto you, and he saith that all is well, then ye will not find fault with him." (Helaman 13:27-28)

"nothing is a greater injury to the children of men than to be under the influence of a false spirit when they think they have the Spirit of God. Thousands have felt the influence of its terrible power and baneful effects. Long pilgrimages have been undertaken, penances endured, and pain, misery and ruin have followed in their train; nations have been convulsed, kingdoms overthrown, provinces laid waste, and blood, carnage and desolation are habiliments in which it has been clothed." (Joseph Smith, HC ch. 33, p. 573)