Obviously, God is the all powerful.
Now of course, Demons are proud creatures, that I doubt they will be announcing they are afraid of God. They will even be waging war with God as stated in the Revelation. So my understanding is there is none in the history and even the bible that says: demons announces they fear God.
But if I am wrong, which are the instances that they stated they fear God? Are there any proofs?
This is the communication between Demons and Jesus (Mat 8:29):
Legion: “What do you want with us, Son of God? Did you come here to torture us before the proper time?”
Legion: “If you drive us out, send us into that herd of pigs.”
Even if it is implied that Jesus has more power over them, they don't even announce or say it out loud.