I used to buy dates from a clan of the Jews called Banu Qaynuqa, then sell them at a profit. News of this reached the Messenger of Allah ﷺ, who said, "Uthman, when you buy, measure it out, and when you sell, measure it out."
كنت أبتاع التمر من بطن من اليهود يقال لهم: بنو قينقاع، فأبيعه بربح، فبلغ ذلك رسول الله ﷺ، فقال: يا عثمان، إذا اشتريت فاكتل، وإذا بعت فكل.
Ahmad (444) narrated it from Abu Saeed, the freedman of Banu Hashim, Ibn Majah (2230) narrated it from the hadith of Abdullah bin Yazid, Abd bin Humayd (52) narrated it from the hadith of Abdullah bin Mubarak, and Bayhaqi (5/315) narrated it from the hadith of Saeed bin Abu Maryam. All of these transmitted from Abdullah bin Lahia, who said, Musa bin Wardan told us, I heard Saeed bin Musayab say, I heard Uthman deliver a sermon from the pulpit saying... and then he mentioned it. Its chain of transmission is hasan because of Ibn Lahia, for those mentioned above heard from him before his memory became confused, and Bayhaqi pointed to this when he said, "Ibn Mubarak, Walid bin Muslim, and a group of senior scholars narrated it from Abdullah bin Lahia." Abu Saeed, the teacher of Ahmad, is named Abdul-Rahman bin Abdullah bin Ubayd Basri. Ahmad and Ibn Main said, He is trustworthy. The wording given is that of Ahmad.The wording of Ibn Majah is, He said, "I used to sell dates in the market, and I would say, 'I measured such and such in this measure of mine,' then I would hand over the dates by that measure and take my price. This troubled me somewhat, so I asked the Messenger of Allah ﷺ, and he said, 'When you have named the measure, then measure it out.'"It has another chain of transmission. Daraqutni (3/8) narrated it, and from him Bayhaqi (5/315-316) narrated it, from the hadith of Abu Salih, who said, Yahya bin Ayub told me, from Ubaydullah bin Mughira, from Munqidh, the freedman of Suraqa, from Uthman bin Affan, that the Messenger of Allah ﷺ said to Uthman, "When you buy, measure it out, and when you sell, measure it out." This chain of transmission is not problematic as a supporting narration. Haythami said, It has also been narrated through another path as a mursal report from Uthman.As for Abu Hatim's statement in al-Ilal (1/383-384), "This is a munkar hadith with this chain of transmission," he qualified this by the specific chain that Ibn Abu Hatim presented, which is what Muhammad bin Himyar narrated, saying, Uzai told me, saying, Thabit bin Thawban told me, saying, Makhul told me, from Abu Qatada, who said, Uthman used to buy food and sell it before taking possession of it, so the Messenger of Allah ﷺ said to him, "When you buy, measure it out, and when you sell, measure it out." This is because Makhul did not hear directly from Abu Qatada.