The Transfiguration of Christ (source)
Your light has sanctified the whole world, as you were transfigured upon the high mountain, O Good One, showing Your power to Your Disciples, that You might deliver the world from transgression. Therefore we cry out to You: O Compassionate Lord, save our souls.
-Idiomelon of the Litia from the Great Feast of the Transfiguration of Christ
(source)
Through the prayers of our Holy Fathers, Lord Jesus Christ our God, have mercy on us and save us! Amen!