Musnad Ahmad 2:198

'Abd al-Rahman narrated to us, 'Abd Allah ibn al-Mubarak narrated to us, from Ma'mar, from al-Zuhri, from al-Sa'ib ibn Yazid, from 'Abd Allah ibn al-Sa'di, who said: 'Umar said to me: "Have I not been informed that you manage some of the people's affairs, and when you are given a wage, you do not accept it?" I said: "Yes." He said: "What do you intend by that?" I said: "I am wealthy; I have slaves and horses. I want my work to be a charity for the Muslims." He said: "Do not do that, for I used to do the same as you are doing. The Messenger of Allah (peace and blessings of Allah be upon him) used to give me a gift, and I would say: 'Give it to someone who is poorer than me.' He said: 'Take it, then either possess it as wealth or give it in charity. Whatever Allah gives you of this wealth, while you are neither coveting it nor asking for it, then take it; and what is not [given in that manner], do not let your soul pursue it.'"