(4) باب زَكَاةِ الْفِطْرِ عَلَى الْمُسْلِمِينَ مِنَ التَّمْرِ وَالشَّعِيرِ
Abu Sa'id al-Khudri reported that when Mu'awiya prescribed half a sa' of wheat equal to one sa' of dates, he (Abu Sa'id al-Khudri) objected to it, and said:
I would take out (Sadaqat-ul-Fitr) but that which I used to bring forth during the lifetime of the Messenger of Allah (ﷺ) one sa' of dates, or one sa' of raisins, or one sa' of barley, or one sa' of cheese.
Reference: Sahih Muslim 985 e
In-book reference: Book 12, Hadith 25
USC-MSA web (English) reference(deprecated numbering scheme): Book 5, Hadith 2158