Excerpt from The Life of St. Antony:

Wherefore the prophet sent by the Lord declared them to be wretched, saying: "Woe is he who giveth his neighbours to drink muddy destruction." For such practices and devices are subversive of the way which leads to virtue. And the Lord Himself, even if the demons spoke the truth,--for they said truly "Thou art the Son of God" --still bridled their mouths and suffered them not to speak lest haply they should sow their evil along with the truth, and that He might accustom us never to give heed to them even though they appear to speak what is true. For it is unseemly that we, having the holy Scriptures and freedom from the Saviour, should be taught by the devil who hath not kept his own order but hath gone from one mind to another. Wherefore even when he uses the language of Scripture He forbids him, saying: "But to the sinner said God, Wherefore dost thou declare My ordinances and takest My covenant in thy mouth ?" For the demons do all things --they prate, they confuse, they dissemble, they confound--to deceive the simple. They din, laugh madly, and whistle; but if no heed is paid to them forthwith they weep and lament as though vanquished.