سنن النسائي

It was narrated that Abu Sa'eed said: "We used to pay Salaqatul Fitr when the Messenger of Allah was among us; a Sa' of food, or a Sa' of dates, or a Sa' of barley, or a Sa' of cottage cheese. We continued to do so until Mu'awiyah came from Ash-Sham and one of the things that he taught the people was when he said: I think that two Mudds of wheat from Ash-Sham are equivalent to a Sa' of this, So the people took to that."