Mark 9:2-13 CSB
After six days Jesus took Peter, James, and John and led them up a high mountain by themselves to be alone. He was transfigured in front of them, and his clothes became dazzling — extremely white as no launderer on earth could whiten them. Elijah appeared to them with Moses, and they were talking with Jesus. Peter said to Jesus, “Rabbi, it’s good for us to be here. Let’s set up three shelters: one for you, one for Moses, and one for Elijah” — because he did not know what to say, since they were terrified.
A cloud appeared, overshadowing them, and a voice came from the cloud: “This is my beloved Son; listen to him!”
Suddenly, looking around, they no longer saw anyone with them except Jesus.
As they were coming down the mountain, he ordered them to tell no one what they had seen until the Son of Man had risen from the dead. They kept this word to themselves, questioning what “rising from the dead” meant.
Then they asked him, “Why do the scribes say that Elijah must come first?”
“Elijah does come first and restores all things,” he replied. “Why then is it written that the Son of Man must suffer many things and be treated with contempt? But I tell you that Elijah has come, and they did whatever they pleased to him, just as it is written about him.”
CSB: Christian Standard Bible