So as Muslims we are grateful for everything done to us by anyone, in return we say may Allah reward you with good (khair). Not thank you which probably doesn’t have any intrinsic meaning other than a kind gesture of good words. (Correct me if I’m wrong)
Our Imaan binds us together as an ummah, so Allah has given us a much better way of showing grace to our fellow Muslims, not only are we grateful and heartfelt we are also wishing them that Allah (swt) rewards them with good!
So what’s the correct way to say it?
Some muslims with the best intentions say:
- Jazak Allah
- Jazak Allah Khair
- Jazak Allahu Khayran / Khairain
- Jazakum Allahu/Jazakumullah Khayr/Khayran
Saying Jazak Allah is incomplete because the sentence says May Allah reward you but it didn’t specify good or bad! Because one may wish bad on something using the same sentence.
Jazak Allahu Khairan is the full sentence if you are saying it to one person male/female. Whilst saying jazak Allahu khair is grammatically not complete. It is most formal to say Jazak Allahu Khayran!
On the other hand if you are addressing more than one person then Jazakumullahu khayran is the correct way to say it. This is not used for to say it to one person.
So Jazak Allahu khayran for one person and Jazakumullahu khayran for a group of people.