Reference: Fataawa Ramadhaan – Volume 2, Page 902, Fatwa No.885
Fataawa as-Siyaam libni Jibreen – Page 188
Question: Is Zakaatul-Fitr obligatory or [just] recommended? And upon whom is it obligatory?
Response: Zakaatul-Fitr is obligatory upon the Muslims because the Prophet (sal-Allaahu ‘alayhi wa sallam) legislated it upon the male and the female and the young and the old. And he specified it to be one saa’ of food or dates or barley or raisins or cheese (one saa’ is equal to four mudd, and one mudd is equal to the amount held by cupping the two hands together. It is a measure by volume and not by weight). And he commanded that it be discharged before the people leave to perform the ‘Eed prayer. So it is a Prophetic obligation which has been legislated for the last part of Ramadhaan as a purification for the fasting one from any mistake or sexual intercourse [which may have come to pass]. And it is food for the needy such that they do not have to wander around asking (begging).
And with Allaah lies all success.