Muwatta Malik, Book 31, Hadith 27 (USC-MSA) ⓘ

Malik said, "The generally agreed on way of doing things among us is that some one who buys some fruit, fresh or dry, should not resell it until he gets full possession of it. He should not barter things of the same type, except hand to hand. Whatever can be made into dry fruit to be stored and eaten, should not be bartered for its own kind, except hand to hand, like for like, when it is the same kind of fruit. In the case of two different kinds of fruit, there is no harm in bartering two of one kind for one of another, hand to hand on the spot. It is not good to set delayed terms. As for produce which is not dried and stored but is eaten fresh like water melon, cucumber, melon, carrots, citron, medlars, pomegranates, and soon, which when dried no longer counts as fruit, and is not a thing which is stored up as is fruit, I think that it is quite proper to barter such things two for one of the same variety hand to hand. If no term enters into it, there is no harm in it."