When we were commanded to give charity, we would hire ourselves out to carry loads. Abu Aqeel came with half a saa, and another man came with more than that. The hypocrites said, "Allah has no need of this man's charity, and this other man did what he did only for show." So this verse was revealed, "Those who criticize the believers who give charity voluntarily, and those who have nothing to give but their own labor" [Tawbah 9:79].
لما أمرنا بالصدقة، كنا نتحامل، فجاء أبو عقيل بنصف صاع، وجاء إنسان بأكثر منه، فقال المنافقون: إن الله لغني عن صدقة هذا، وما فعل هذا الآخر إلا رياء، فنزلت: {يلمزون المطوعين من المؤمنين في الصدقات والذين لا يجدون إلا جهدهم} الآية.
Bukhari related it in the tafsir chapter (4668), and Muslim in the zakat chapter (1018), both by way of Bishr bin Khalid Abu Muhammad, who said, Muhammad bin Jafar informed us, from Shubah, from Sulayman, from Abu Waail, from Abu Masud, who said, and then he narrated it. The wording given is Bukhari's.In another version found in Bukhari's tafsir chapter (4669), by a different route from Sulayman, with this wording, the Messenger of Allah ﷺ used to command giving charity, and one of us would strive hard until he managed to bring a measure of grain, whereas today one of them may have a hundred thousand. It was as though he was hinting about himself.