The literature of the New Testament is just some of the textual data that not only affirms this fact, but is the basis for it. By the time these texts are written, evil, illnesses, and bad things were already assigned to a separate agent, variously presented as Satan, Beelzebub, etc. ...
23 And all the people were amazed, and said, Is not this the son of David? 24 But when the Pharisees heard it, they said, This fellow doth not cast out devils, but by Beelzebub the prince of the devils. 25 And Jesus knew their thoughts, and said unto them, Every kingdom divided...