"I heard 'Umar say: "The Messenger of Allah ﷺ, said: 'Gold for silver is usury, unless it is exchanged on the spot."' (Sahih) Abu Bakr bin Abu-Shaibah said: "I heard sufyan saying: 'Gold for silver." memorize (this).
قَالَ رَسُولُ اللَّهِ ﷺ الذَّهَبُ بِالْوَرِقِ رِبًا إِلاَّ هَاءَ وَهَاءَ قَالَ أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ سَمِعْتُ سُفْيَانَ يَقُولُ الذَّهَبُ بِالْوَرِقِ احْفَظُوا