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bukhari:1505Qabīṣah > Sufyān > Zayd b. Aslam > ʿIyāḍ b. ʿAbdullāh > Abū Saʿīd

We used to give one Sa' of barley as Sadaqat-ul-Fitr (per head).  

البخاري:١٥٠٥حَدَّثَنَا قَبِيصَةُ حَدَّثَنَا سُفْيَانُ عَنْ زَيْدِ بْنِ أَسْلَمَ عَنْ عِيَاضِ بْنِ عَبْدِ اللَّهِ عَنْ أَبِي سَعِيدٍ ؓ قَالَ

كُنَّا نُطْعِمُ الصَّدَقَةَ صَاعًا مِنْ شَعِيرٍ