It is narrated from Bilal bin Rabah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Hold fast to the night prayer, for it is the habit of the righteous people before you, a means of nearness to Allah, an expiation for faults, it restrains from sins, and it is a means of keeping disease away from the body."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4650