The Book of Zakat (Kitab Al-Zakat)
Muslim :: Book 5 : Hadith 2256
Abu Umama reported Allah's Messenger (may peace be upon him) as saying: 0 son of Adam, it is better for you if you spend your surplus (wealth), but if you withhold it, it is evil for you. There is (however) no reproach for you (if you withhold means necessary) for a living. And begin (charity) with your dependants; and the upper hand is better than the lower hand.