Russian traditional performed by the Don Cossack Choir.
Clip contains a German translation. Here you have a brief English one:
This is the story of the twelve blood-thirsty robbers told by Monk Peterim at Solovki. Led by their Captain Kudejar the gang killed many faithful Christians; they stole many treasures and lived in a dark wood. But one day the Lord enlightened the heart of the cruel Kudejar. He left his gang, bid farwell to the world and retired to a monastery.