Jami At Tirmidhi
675
Sahih+3

Ibn Umar narrated:"The Messenger of Allah made Sadaqatul-Fitr an obligation upon the male and female, the free and the bondsmen, as a Sa of dried dates or a Sa of barley." He said: "So the people equated that to half a Sa of wheat

SahihAhmad Muhammad Shakir
SahihAl-Albani