Ruling on currency exchange with part of the amount remaining for a later time

السؤال:
The first message in this episode is from Abha. The sender is the listener 'Umar ibn Ahmad. The brother 'Umar says in one of his questions: I work in a shop, and sometimes my neighbor comes to me and says, "Exchange fifty riyals for me." At that time, I might only have, for example, thirty. So I tell him, and he says, "Take the fifty, give me the thirty, and I will owe you twenty." Is this permissible or not? May Allah reward you with good.
Answer:
In the name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, and may Allah send prayers and blessings upon the Messenger of Allah, and upon his family and his Companions, and upon those who follow his guidance. As for what follows:
This transaction is not permissible because it involves taking possession of part of the amount and deferring the rest. Currency exchange must be hand-to-hand. The correct method is for him to give you the fifty as a trust in your possession, and you take the thirty as a loan. Then, you settle the account with him until he gives you the fifty, or you return the thirty to him. Either you sell him the fifty and give him the remaining twenty hand-to-hand, and settle the account for the thirty, or you return the thirty to him and take the fifty.
The point is that this is a sale that is only valid hand-to-hand. Exchanging thirty for fifty is not permissible. However, the fifty can be held as a trust, and he can take the thirty as a loan, and there is no blame in that. Yes.

The presenter : May Allah reward you with good, and may He do you good.