Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "There is no good in trade, except for the one who does not (unduly) praise what he sells, does not disparage what he buys, earns what is lawful and gives what is lawful, and keeps away from swearing oaths in it."
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains Umar bin Rashid, whom al-Ijli declared thiqah (trustworthy), while the majority declared him da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب البيوع / 6300