Maliks Muwatta Book 17, Hadith Number 55.

Section : Who Pays the Zakat al-Fitr.

Yahya related to me from Malik from Nafi that Abdullah ibn Umar would always pay the zakat al-fitr in dates, except once, when he paid it in barley.

Maliksaid, “Payment of all types of kaffara, of zakat al-fitr and of the zakat on grains for which a tenth or a twentieth is due, is made using the smaller mudd, which is the mudd of the Prophet, may Allah bless him and grant him peace, except in the case of dhihar divorce, when the kaffara is paid using the mudd of Hisham, which is the larger mudd.”