Revelation 4:6
And there was an ocean, as crystal-clear as glass, in front of the throne. And at the center, surrounding the throne were four living beings, covered with eyes in the front and back of them. [Note: In view of Isa. 6:1-3 and especially Eze. 10:20ff, these "living beings" appear to be some special order of heavenly beings who inhabit the presence of God].
Revelation 4:8
And each of the four living beings had six wings [and] were covered with eyes all around them and [even] within them. And day and night they never stop saying, [Note: Some translations have "singing" here and at other places below], "Holy, holy, holy [is] the Lord God Almighty, who was [in the past] and who is [in the present] and who will come [in the future]."