Unclean Spirit
The Lord tells Israel:
Zechariah 13:2 And it shall come to pass in that day, saith the LORD of hosts, that I will cut off the names of the idols out of the land, and they shall no more be remembered: and also I will cause the prophets and the unclean spirit to pass out of the land.
2 times in Matthew: Matthew 10:1, 12:43
10 times in Mark: Mark 1:23,26-27, 3:11,30, 5:2,8,13, 6:7, 7:25,
6 times in Luke: Luke 4:33,36, 6:18, 8:29, 9:42, 11:24
2 times in Acts: Acts 5:16, 8:7
2 times in Revelation: Revelation 16:13, 18:2
Evil Spirit
God allowed these events to occur:
Judges 9:23 Then God sent an evil spirit between Abimelech and the men of Shechem; and the men of Shechem dealt treacherously with Abimelech:
1 Samuel 16:14-16,23 But the Spirit of the LORD departed from Saul, and an evil spirit from the LORD troubled him. And Saul’s servants said unto him, Behold now, an evil spirit from God troubleth thee. Let our lord now command thy servants, which are before thee, to seek out a man, who is a cunning player on an harp: and it shall come to pass, when the evil spirit from God is upon thee, that he shall play with his hand, and thou shalt be well. … And it came to pass, when the evil spirit from God was upon Saul, that David took an harp, and played with his hand: so Saul was refreshed, and was well, and the evil spirit departed from him.
1 Samuel 18:10 And it came to pass on the morrow, that the evil spirit from God came upon Saul, and he prophesied in the midst of the house: and David played with his hand, as at other times: and there was a javelin in Saul’s hand.
1 Samuel 19:9 And the evil spirit from the LORD was upon Saul, as he sat in his house with his javelin in his hand: and David played with his hand.
The Lord, during His earthly ministry, casts them out:
Luke 7:21 And in that same hour he cured many of their infirmities and plagues, and of evil spirits; and unto many that were blind he gave sight.
Luke 8:2 And certain women, which had been healed of evil spirits and infirmities, Mary called Magdalene, out of whom went seven devils,
Paul had to deal with them:
Acts 19:12-13,15-16 So that from his body were brought unto the sick handkerchiefs or aprons, and the diseases departed from them, and the evil spirits went out of them. Then certain of the vagabond Jews, exorcists, took upon them to call over them which had evil spirits the name of the LORD Jesus, saying, We adjure you by Jesus whom Paul preacheth. … And the evil spirit answered and said, Jesus I know, and Paul I know; but who are ye? And the man in whom the evil spirit was leaped on them, and overcame them, and prevailed against them, so that they fled out of that house naked and wounded.
Demon – Devils – Evil Spirit – Unclean Spirit are all mentioned in the Scripture.
Believers should have nothing to do with them.