Metamorphoses Book 10: Orpheus and Eurydice
"'To you (Pluto) are owed / Ourselves and all creation: a brief while / We linger; then we hasten, late or soon, / To one abode; here one road leads us all; / Here in the end is home; over humankind / Your kingdom keeps the longest sovereignty. / She too, when ripening years reach their due term, / Shall own your rule. The favour that I ask / Is but to enjoy her love'" Book 10 -- Orpheus and Eurydice, line 31-9.
Pluto, ruler of the Underworld, agreed to let Eurydice go back to the living as long as Orpheus didn't turn back to look at her until they were completely out of Hades. When the light of the world was beginning to show, Orpheus turned back and looked at his bride and she slipped away back into Hell and he couldn't get her back. For three years Orpheus mourned his wife and would only love small boys. He would play his songs in the forests and charm the trees and animals around him.