The translation of Dante that Thom Yorke seems to have used in this quote is Sinclair’s:
‘Now must thou thus cast off all sloth,’ said the Master ‘for sitting on down or under blankets none comes to fame, and without it he that consumes his life leaves such trace of himself on earth as smoke in air or foam on the water. Rise, therefore, conquer thy panting with the soul, which conquers in every battle if it sink not with its body’s weight. There is a longer stair which must be climbed’ (XXIV, pg. 297)
Dante Alighieri, The Divine Comedy, I: Inferno, trans. John D. Sinclair (NY: Oxford UP, 1959)
This translation was first published in 1939.