Although he finally chose not to use it, the draft version of the epigraph for the poem came from Dante's Purgatorio (XXVI, 147-148):
'sovegna vos a temps de ma dolor'.
Poi s'ascose nel foco che gli affina.
Eliot provided this translation in his essay "Dante" (1929):
'be mindful in due time of my pain'.
Then dived he back into that fire which refines them.