Sayyiduna Abu Umamah al-Bahili (may Allah be pleased with him) says 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 before you, a means of nearness to Allah Almighty, an expiation for sins, and it restrains from sins."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4648