Yahya bin 'Abdullah bin Muhammad يحيى بن عبد الله بن محمد · The Book of Zakah

"At the time of the Messenger of Allah, we used to give a Sa' of barley, or dates, or raisins, or cottage cheese, and we continued to do so until the time of Mu'awiyah, when he said: 'I think that two Mudds of wheat from Ash-Sham are equivalent to a Sa' of barley."'