It was narrated from Hafs bin 'Asim, from Abu Hurairah that the Prophet forbade two kids of transactions:
Munabadhah and Mulamasha. And he said that Mulamasah means when one man says to another: "I will sell you my garment for your garment," and neither of them looks at the garment of the others, rather he just touches it. And Munabadhah is when he says: "I will throw what I have and you throw what you have," so that they buy from one another, and neither of them knows how much the other has, and so on.
Reference: Sunan an-Nasa'i 4517 In-book : Book 44, Hadith 69 English translation : Vol. 1, Book 8, Hadith 4521
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