"Ibn 'Umar and I went to Abu Sa'eed and he narrated to us: 'the Messenger of Allah ﷺ said - and I heard him with these [two] ears: "Do not sell gold for gold except kind for kind, nor sliver for silver except kind for kind, do not exchange more of one than the other, and do not sell what is not present from them for what is present."
انْطَلَقْتُ أَنَا وَابْنُ عُمَرَ إِلَى أَبِي سَعِيدٍ فَحَدَّثَنَا أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ سَمِعَتْهُ أُذُنَاىَ هَاتَانِ يَقُولُ لاَ تَبِيعُوا الذَّهَبَ بِالذَّهَبِ إِلاَّ مِثْلاً بِمِثْلٍ وَالْفِضَّةَ بِالْفِضَّةِ إِلاَّ مِثْلاً بِمِثْلٍ لاَ يُشَفُّ بَعْضُهُ عَلَى بَعْضٍ وَلاَ تَبِيعُوا مِنْهُ غَائِبًا بِنَاجِزٍ