It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Hold fast to huzn (sorrow and grief), for it is the key to the heart." The Companions said: O Messenger of Allah, how is huzn attained? He (peace and blessings be upon him) said: "Keep yourselves hungry and thirsty."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11644