Sunan an Nasai
2512
Sahih+2

It was narrated that Ibn 'Abbas said:"We used to pay Zakaul Fitr when the Messenger of Allah was among us; a Sa' of food, or a Sa' of barley, or a Sa' of dates, or a Sa' of raisins, or a Sa of cottage cheese

SahihAbu Ghuddah
SahihAl-Albani