Tertullian

The Father gave to the Son new disciples after Moses and Elijah had been exhibited along with him in the honor of his glory and had then been dismissed as having fully discharged their duty and office.… But we have the entire structure of this same vision in Habakkuk also, where the spirit in the person of some of the apostles says, “O Lord, I have heard your speech and was afraid.” What speech was this, other than the words of the voice from heaven, “This is my beloved Son, hear him”? “I considered your works and was astonished.” When could this have better happened than when Peter, on seeing his glory, knew not what he was saying? “In the midst of the two you shall be known”—even Moses and Elijah.