Qatadah narrates from al-Hasan al-Basri (may Allah have mercy on him) that he said regarding the zakah of Ramadan (sadaqat al-fitr): "Upon whoever fasted, there is a sa' of dates or of wheat."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7708