Mark 9:5
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.
Cross-reference
John 14:9
Allusion
In John 14:9, Jesus says seeing him is seeing the Father — this is exactly what Peter witnesses on the mountain: Jesus' divine glory.
Matthew 17:4
Parallel
Matthew 17:4 is the parallel account of Peter's identical words at the Transfiguration.
Luke 9:33
Parallel
Luke 9:33 records the same event, with Peter's words and the added note that he did not know what he was saying.