Muwatta Malik, Book 31, Hadith 1322 (In-Book) ⓘ

Yahya related to me from Malik from Humayd ibn Qays al-Makki that Mujahid said, "I was with Abdullah ibn Umar and an artisan came to him and said, 'Abu Abd ar-Rahman - I fashion gold and then sell what I have made for more than its weight. I take an amount equivalent to the work of my hand.' Abdullah forbade him to do that, so the artisan repeated the question to him, and Abdullah continued to forbid him until he came to the door of the mosque or to an animal that he intended to mount. Then Abdullah ibn Umar said, 'A dinar for a dinar, and a dirham for a dirham. There is no increase between them. This is the command of ourProphet to us and our advice to you.' "

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ حُمَيْدِ بْنِ قَيْسٍ الْمَكِّيِّ، عَنْ مُجَاهِدٍ، أَنَّهُ قَالَ كُنْتُ مَعَ عَبْدِ اللَّهِ بْنِ عُمَرَ فَجَاءَهُ صَائِغٌ فَقَالَ لَهُ يَا أَبَا عَبْدِ الرَّحْمَنِ إِنِّي أَصُوغُ الذَّهَبَ ثُمَّ أَبِيعُ الشَّىْءَ مِنْ ذَلِكَ بِأَكْثَرَ مِنْ وَزْنِهِ فَأَسْتَفْضِلُ مِنْ ذَلِكَ قَدْرَ عَمَلِ يَدِي ‏.‏ فَنَهَاهُ عَبْدُ اللَّهِ عَنْ ذَلِكَ فَجَعَلَ الصَّائِغُ يُرَدِّدُ عَلَيْهِ الْمَسْأَلَةَ وَعَبْدُ اللَّهِ يَنْهَاهُ حَتَّى انْتَهَى إِلَى بَابِ الْمَسْجِدِ أَوْ إِلَى دَابَّةٍ يُرِيدُ أَنْ يَرْكَبَهَا ثُمَّ قَالَ عَبْدُ اللَّهِ بْنُ عُمَرَ الدِّينَارُ بِالدِّينَارِ وَالدِّرْهَمُ بِالدِّرْهَمِ لاَ فَضْلَ بَيْنَهُمَا هَذَا عَهْدُ نَبِيِّنَا إِلَيْنَا وَعَهْدُنَا إِلَيْكُمْ ‏.‏