Ishaq bin Mansur al-Kausaj إسحاق بن منصور بن بهرام - الكوسج · The Chapters on Business Transactions

"I bear witness that the true and truly inspired one Abul-Qasim (ﷺ) told us: 'Selling a Muhaffalah is Khilabah, and Khilabah is not lawful for the Muslim."' (Ibn Majah said: " Meaning: 'Deception.")

'(Sell) silver for silver, gold for gold, barley for barley, wheat for wheat, like for like."