Al-Muwatta de Malik, 629

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." Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to send the zakat al-fitr to the one with whom it was collected together two or three days before the day of breaking the fast