that his father said, "The Prophet ﷺ forbade the selling of gold for gold and silver for silver except if they are equivalent in weight, and allowed us to sell gold for silver and vice versa as we wished." (Using translation from Bukhārī 2182)
نَهَانَا رَسُولُ اللهِ ﷺ عَنْ بَيْعِ الْفِضَّةِ بِالْفِضَّةِ وَالذَّهَبِ بِالذَّهَبِ إِلَّا سَوَاءً بِسَوَاءٍ وَأَمَرَنَا أَنْ نَبْتَاعَ الذَّهَبَ فِي الْفِضَّةِ كَيْفَ شِئْنَا وَالْفِضَّةَ بِالذَّهَبِ كَيْفَ شِئْنَا