How did the disciples recognize Moses and Elijah on the mount of transfiguration?

1b Jesus took with him Peter and James, and John his brother, and led them up a high mountain by themselves. 2 And he was transfigured before them, and his face shone like the sun, and his clothes became white as light. 3 And behold, there appeared to them Moses and Elijah, talking with him. 4 And Peter said to Jesus, “Lord, it is good that we are here. If you wish, I will make three tents here, one for you and one for Moses and one for Elijah.”

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5 He was still speaking when, behold, a bright cloud overshadowed them, and a voice from the cloud said, “This is my beloved Son, with whom I am well pleased; listen to him.” 6 When the disciples heard this, they fell on their faces and were terrified. 7 But Jesus came and touched them, saying, “Rise, and have no fear.” 8 And when they lifted up their eyes, they saw no one but Jesus only.
9 And as they were coming down the mountain, Jesus commanded them, “Tell no one the vision, until the Son of Man is raised from the dead.”

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