سنن أبي داود

Ibn al-Saidi said : Umar employed me to collect the sadaqah. When I finished doing so and gave it to him, he ordered payment to be given to me. I said: I did only for Allah’s sake, and my reward will come from Allah. He said: Take what you are given, for I acted (as a collector) during the time of the Messenger of Allah (May peace be upon him) and he assigned me a payment. Thereupon, I said the same kind of thing as you have said, to which Messenger of Allah (May peace be upon him) said: When you are given something without asking for it, you should use it for your own purpose and as sadaqah.