Muwatta Malik, Book 17, Hadith 54 (USC-MSA)

Yahya related to me from Malik from Zayd ibn Aslam from lyad ibn Abdullah ibn Sad ibn Abi Sarh al-Amiri that he had heard Abu Said al- Khudri say, "We used to pay the zakat al-fitr with a sa of wheat, or a sa of barley, or a sa of dates, or a sa of dried sour milk, or a sa of raisins, using the sa of the Prophet, may Allah bless him and grant him peace. "

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ عِيَاضِ بْنِ عَبْدِ اللَّهِ بْنِ سَعْدِ بْنِ أَبِي سَرْحٍ الْعَامِرِيِّ، أَنَّهُ سَمِعَ أَبَا سَعِيدٍ الْخُدْرِيَّ، يَقُولُ كُنَّا نُخْرِجُ زَكَاةَ الْفِطْرِ صَاعًا مِنْ طَعَامٍ أَوْ صَاعًا مِنْ شَعِيرٍ أَوْ صَاعًا مِنْ تَمْرٍ أَوْ صَاعًا مِنْ أَقِطٍ أَوْ صَاعًا مِنْ زَبِيبٍ وَذَلِكَ بِصَاعِ النَّبِيِّ صلى الله عليه وسلم ‏.‏

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also referenced under: Book 17, Hadith 630 (In-Book)