Hadith #2609 (Sunan al-Nasa'i)
Book: The Book of Zakah
Narrator(s): Abd al-Muttalib b. Rabi'ah b. al-Harith, Abdullah bin Wahb عبد الله بن وهب بن مسلم القرشي, al-Zuhri ابن شهاب الزهري‎, محمد بن مسلم, Amr bin Sawad عمرو بن سواد, Yonus bin Yazid bin Abi al-Nijad يونس بن يزيد بن أبي النجاد

“Umar bin Al-Khattab, may Allah be pleased with him, appointed me in charge of the Sadaqah. When I finished collecting it and handed it over to him, he ordered that I be given some payment. I said to him: ‘I only did for the sake of Allah, the Mighty and Sublime, and my reward will be with Allah, the Mighty and Sublime.’ He said: ‘Take what I have given you: I did the same take during the time of the Messenger of Allah, and I said what you have said, but the Messenger of Allah said to me: “If you are given something without asking for it, then keep (some) and give (some) in charity.”‘

Source: https://parallelquran.com/hadith/sunan-al-nasai-2609/