Imam Malik's Muwatta, Chapter: Business Transactions

Malik said, "It is the generally agreed on way of doing things among us that the meat of camels, cattle, sheep and so on is not to be bartered one for one, except like for like, weight for weight, from hand to hand. There is no harm in that. If it is not weighed, then it is estimated to be like for like from hand to hand." Malik said, "There is no harm in bartering the meat of fish for the meat of camels, cattle, and sheep and so on two or more for one, from hand to hand. If delayed terms enter the transaction however, there is no good in it." Malik said, "I think that poultry is different from the meat of cattle and fish. I see no harm in selling some of it for something different, more of one than another, from hand to hand. None of that is to be sold on delayed terms."