Revelation 14:2-3

And I heard a voice from heaven, like the sound of great waters and like the rumbling of mighty thunder; and the voice that I heard [seemed like music and] was like the sound of harpists playing on their harps. And they sang a new song before the throne [of God] and before the four living creatures and the elders; and no one could learn the song except the hundred and forty-four thousand who had been purchased (ransomed, redeemed) from the earth. [Rev 7:4-8]