[Machine] Buy it and then trade it for barley. So the boy went and took a measure and some extra of it. When Ma'mar came, he informed him about it, so Ma'mar said to him, "Why did you do this? Go and return it, do not take anything except the same in return, for I used to hear the Messenger of Allah ﷺ saying, ‘Food is equal to its like.’ And at that time our food was barley, so it was said that it was not equal to it, so he (the Prophet ﷺ) said, ‘I fear that it might become close to riba.’"
بِعْهُ ثُمَّ اشْتَرِ بِهِ شَعِيرًا فَذَهَبَ الْغُلَامُ فَأَخَذَ صَاعًا وَزِيَادَةَ بَعْضِ صَاعٍ فَلَمَّا جَاءَ مَعْمَرٌ خَبَّرَهُ بِذَلِكَ فَقَالَ مَعْمَرٌ لِمَ فَعَلْتَ؟ انْطَلِقْ فَرُدَّهُ لَا تَأْخُذَنَّ إِلَّا مِثْلاً بِمِثْلٍ فَإِنِّي كُنْتُ أَسْمَعُ رَسُولَ اللهِ ﷺ يَقُولُ «الطَّعَامُ مِثْلًا بِمِثْلٍ» وَكَانَ طَعَامَنَا يَوْمَئِذٍ الشَّعِيرُ فَقِيلَ إِنَّهُ لَيْسَ مِثْلَهُ فَقَالَ إِنِّي أَخَافُ أَنْ يُضَارِعَ الرِّبَا