Origen
Catena Aurea · Markusevangelium 9
And he said unto them, Verily I say unto you, That there be some of them that stand here, which shall not taste of death, till they have seen the kingdom of God come with power. And after six days Jesus taketh with him Peter, and James, and John, and leadeth them up into an high mountain apart by themselves: and he was transfigured before them. And his raiment became shining, exceeding white as snow; so as no fuller on earth can white them. And there appeared unto them Elias with Moses: and they were talking with Jesus. And Peter answered and said to Jesus, Master, it is good for us to be here: and let us make three tabernacles; one for thee, and one for Moses, and one for Elias. For he wist not what to say; for they were sore afraid. And there was a cloud that overshadowed them; and a voice came out of the cloud, saying, This is my beloved Son: hear him. And suddenly, when they had looked round about, they saw no man any more, save Jesus only with themselves.
(in Matt tom. xii. 40) Mark says in his own person, For he wist not what to say. Where it is matter for, consideration, whether perchance Peter spoke this in the confusion of his mind, by the motion of a spirit not his own; whether perchance that spirit himself who wished, as far as in him lay, to be a stumbling-block to Christ, so that He might shrink from that Passion, which was the saving of all men, did not here work as a seducer and wish under the colour of good to prevent Christ from condescending to men, from coming to them, and taking death upon Himself for their sakes.