Origen — as excerpted in the Catena Aurea on Mark 9:9-13

“(in Matt. tom. xii. 43) After the shewing of the mystery on the mount, the Lord commanded His disciples, as they were coming down from the mount, not to reveal His transfiguration, before the glory of His Passion and Resurrection; wherefore it is said, And as they came down from the mountain, he charged them that they should tell no man what things they had seen, till the Son of man were risen from the dead.”