What is the ruling of deferred change after purchasing an item?

Question:

I wanted to clarify regarding your fatwa (What is the ruling on exchanging Rands for Rands? – Posted on June 4, 2013).
1) We usually face such situation (used to in past) like when I have 1000rs and bought a thing worth 50rs. The shopkeeper has only change of 650rs to return now and we agree that he will pay me the rest 300rs
later.

Does this also fall under same fatwa that you gave ?..Also, can the above situation and also the one asked in rands exchange question be considered as a loan (i.e. in my case he has taken a loan of 300rs) ?
JazakAllah Khairan for your time and efforts and please remember me and my family in your duas.

Answer:

In the Name of Allah, the Most Gracious, the Most Merciful.

As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.

50 Rand from the 1000 you forwarded were in lieu of the item.  950 Rand were not in lieu of anything.  Whatever amount remains in the shopkeepers possession is an Amānah (trust).[1]
This transaction will not be regarded as a currency exchange as the currency was not the primary traded commodity.
It cannot be regarded as a loan either, or else this will result in two transactions tied together which is prohibited in Sharī’ah.

And Allah Ta’ālā Knows Best

Mufti Faraz Adam,
www.darulfiqh.com