What is the ruling on postponing the receipt of the remaining money in a purchasing transaction where the item has been received and the full price paid, but the seller does not have change, and is this considered usury due to the lack of hand-to-hand exchange?

Scholars differ on the ruling concerning the buyer leaving the remainder of his money with the seller. One group permits it, considering it a trust (amanah), citing a fatwa from the Permanent Committee. Another group prohibits it, considering it a combination of a sale and currency exchange (sarf), citing a fatwa from Sheikh Muhammad ibn Salih al-Uthaymin. The more preponderant opinion is that of permissibility, because currency exchange is not intended in this case, and due to the lack of scholarly consensus on the impermissibility of combining a sale and currency exchange in one contract. Furthermore, the Malikis permit this because the small amount involved indicates that their combination is not intended.