Ante-Nicene Fathers, Vol VIII:
Pseudo-Clementine Literature.: Chapter XXII

Chapter XXII.—Why They Sometimes Come True.

“But if any one say, What is the use of this, that they should be permitted even sometimes to speak truth, and thereby so much error be introduced amongst men? let him take this for answer:  If they had never been allowed to speak any truth, then they would not foretell anything at all; while if they did not foretell, they would not be known to be demons.  But if demons were not known to be in this world, the cause of our struggle and contest would be concealed from us, and we should suffer openly what was done in secret, that is, if the power were granted to them of only acting against us, and not of speaking.  But now, since they sometimes speak truth, and sometimes falsehood, we ought to acknowledge, as I have said, that their responses are of demons, and not of God, with whom there is never falsehood.