The Synoptic Gospels have slightly different versions of the Transfiguration of Christ. Luke has Jesus inviting Peter, James, and John up the mountain to pray. His Transfiguration took place when He was at prayer. His garments became dazzling white. Moses and Elijah appeared and were conversing with Jesus. Then, a cloud came and from the cloud came a voice that said, "This is my beloved Son; listen to him." After the voice had spoken, Jesus was there alone and told his three friends not to tell anyone at that time what they had seen.
Peter will later write about it in his letter as it was a tremendous experience for them. It must have been a very consoling moment for Jesus. He will take the same three friends into the garden when he prays in agony before his Passion.