"At the time of the Messenger of Allah, the people used to give as Sadaqatul Fitr a Sa' of barely or dates or rye or raising."
Sunan an-Nasa'i Book 23, Hadith 82
← Previous Hadith "Give Zakah of your fast." The people started looking at one another. So he said: "Whoever is here of the people of Al-Madinah, get up and teach your brothers, for they do not know that the Messenger of Allah has enjoined Salaqatul Fitr upon young and old, free and slave, male and female; half a Sa' of wheat or a Sa' of dates or barely." Al_Hasan said: 'If Allah has given you more, then give more generously of wheat or something else."'

Sunan an-Nasa'i Book 23, Hadith 81 Next Hadith → "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."'

Sunan an-Nasa'i Book 23, Hadith 83