There is mention in Hadith about the reward of refunding (اقالة) a Muslim brother. What if a Muslim refunds a non-Muslim? Will he get the same reward?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
The Prophet ﷺ is reported to have said: "Whoever agrees with a Muslim to cancel a transaction, Allāh will forgive his sins on the Day of Resurrection."
This ḥadīth is referring to the following scenario: a person purchases something from another and the transaction is finalized, but the buyer then regrets the purchase for some reason and he tries to return it to the seller, and the seller then accepts the return and refunds the buyer out of kindness even though he does not have to.
Imām al-Ṣanaʻānī has argued that in such narrations unless the term implies a restriction to Muslims only, it is considered universal. This ḥadīth would be an example of a situation where the restriction to Muslims is not implied, and in this scenario, allowing a non-Muslim to reverse a transaction due to their regret is considered an act of kindness and a part of universal good ethics. We can hope for a similar reward from Allāh if we perform such an act with the best intentions and in the best manner, whether the other party is Muslim or non-Muslim.
Only Allah knows best
Written by Shaykh Umer Khan
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Sunan Abū Dāwūd, ḥadīth 3640; Sunan Ibn Mājah, ḥadīth 219