Revelation 4:6, 8

Also in front of the throne there was what looked like a sea of glass, clear as crystal. In the center, around the throne, were four living creatures, and they were covered with eyes, in front and in back.

Each of the four living creatures had six wings and was covered with eyes all around, even under its wings. Day and night they never stop saying: “ ‘Holy, holy, holy is the Lord God Almighty,’ who was, and is, and is to come.”