Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Allah Almighty says: 'When I test My servant through his two beloved things (his eyes) and he is patient, then in return for them I will grant him Paradise.'"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6552