From Sahih Muslim (Hadith 2408):
Ibn al-Sa'di Maliki reported:'Umar b. Khattab (Allah be pleased with him) appointed me as a collector of Sadaqa. When I had finished that (the task assigned to me) and I handed over that to him (to 'Umar), he commanded me to (accept) some remuneration (for the work). I said: I performed this duty for Allah and my reward is with Allah. He said: Take whatever has been given to you, for I also performed this duty during the time of the Messenger of Allah (ﷺ). He assigned me the task of a collector and I said as you say, and the Messenger of Allah (ﷺ) said to me: When you are given anything without your begging for it, (then accept it), eat it and give it in charity
Reference: Muslim 2408