While he was still speaking, a cloud formed and cast its shadow over them, and they were afraid as they entered the cloud.
In context
32Peter and his companions were heavy with sleep, but they came fully awake and saw his glory and the two men standing with him. 33As these were leaving him, Peter said to Jesus, “Master, it is good that we are here. Let us put up three shelters, one for you, one for Moses and one for Elijah” — not knowing what he was saying. 34While he was still speaking, a cloud formed and cast its shadow over them, and they were afraid as they entered the cloud. 35And a voice came out of the cloud: “This is my Son, the Chosen One. Listen to him.” 36When the voice had spoken, Jesus was found alone. The disciples kept silent, and in those days they told no one anything of what they had seen.