Sunan an-Nasa'i 2604
It was narrated that Ibn As-Sa'idi Al-Maliki said:
"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."'
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ بُكَيْرٍ، عَنْ بُسْرِ بْنِ سَعِيدٍ، عَنِ ابْنِ السَّاعِدِيِّ الْمَالِكِيِّ، قَالَ اسْتَعْمَلَنِي عُمَرُ بْنُ الْخَطَّابِ رضى الله عنه عَلَى الصَّدَقَةِ فَلَمَّا فَرَغْتُ مِنْهَا فَأَدَّيْتُهَا إِلَيْهِ أَمَرَ لِي بِعُمَالَةٍ فَقُلْتُ لَهُ إِنَّمَا عَمِلْتُ لِلَّهِ عَزَّ وَجَلَّ وَأَجْرِي عَلَى اللَّهِ عَزَّ وَجَلَّ ‏.‏ فَقَالَ خُذْ مَا أَعْطَيْتُكَ فَإِنِّي قَدْ عَمِلْتُ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَقُلْتُ لَهُ مِثْلَ قَوْلِكَ فَقَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ إِذَا أُعْطِيتَ شَيْئًا مِنْ غَيْرِ أَنْ تَسْأَلَ فَكُلْ وَتَصَدَّقْ ‏"‏ ‏.‏