Sahih Bukhari Volume 004, Book 053, Hadith Number 371.

Narated By Urwa bin Az-Zubair : Hakim bin Hizam said, "I asked Allah's Apostle for something, and he gave me. I asked him again, and he gave me, and said to me. 'O Hakim! This wealth is like green sweet (i.e. fruit), and if one takes it without greed, then one is blessed in it, and if one takes it with greediness, then one is not blessed in it, and will be like the one who eats without satisfaction. And an upper (i.e. giving) hand is better than a lower (i.e. taking) hand,' I said, 'O Allah's Apostle! By Him Who has sent you with the Truth. I will not ask anyone for anything after you till I leave this world." So, when Abu Bakr during his Caliphate, called Hakim to give him (some money), Hakim refused to accept anything from him. Once 'Umar called him (during his Caliphate) in order to give him something, but Hakim refused to accept it, whereupon 'Umar said, "O Muslims! I give him (i.e. Haklm) his right which Allah has assigned to him) from this Fai '(booty), but he refuses to take it." So Haklm never took anything from anybody after the Prophet till he died.