2 Besides, you have in your Book of Daniel the account of the three youths, which you will find it difficult to reconcile with the opinion that to abstain from meats is the doctrine of devils. For we are told that they abstained not only from what the law forbade, but even from what it allowed; and you are wont to praise them, and count them as martyrs; though they too followed the doctrine of devils, if this is to be taken as the apostle's opinion. And Daniel himself declares that he fasted for three weeks, not eating flesh or drinking wine, while he prayed for his people. How is it that he boasts of this doctrine of devils, and glories in the falsehood of a lying spirit?
Source: Reply to Faustus the Manichaean (New Advent)