Wardan al-Rumi asked Ibn Umar (may Allah be pleased with them both): I make jewellery, then I sell it and take something extra for it in return for my wages or the work of my hands. Ibn Umar (may Allah be pleased with them both) said: Gold for gold; there is no excess (tafadul) in it. This is the covenant our companion took from us, and this is our covenant to you. Imam al-Shafi'i (may Allah have mercy on him) said: By "companion" he meant Sayyiduna Umar bin al-Khattab (may Allah be pleased with him).
In al-Muzani's narration from him, al-Shafi'i narrated the story of the goldsmith at length and then said: This is a mistake.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10493