Musnad Abu Ya'la al-Mawsili 128:27

Zuhayr narrated to us, Yunus bin Muhammad narrated to us, Layth bin Sa’d narrated to us, from Yazid bin al-Had, from ‘Amr, from Anas, who said: I heard the Messenger of Allah (ﷺ) say: Allah said: "If I afflict My servant with his two beloved ones, then he shows patience, I will compensate him for them with Paradise." He meant his two eyes.