I shall always pay one sa'. We used to pay during the lifetime of the Messenger of Allah ﷺ one sa' of dried dates or of barley, or of cheese, or of raisins. This is the version of Yahya. Sufyan added in his version: "or one sa' of flour." The narrator Hamid (ibn Yahya) said: The people objected to this (addition); Sufyan then left it. Abu Dawud said: This addition is a misunderstanding on the part of Ibn Uyainah.  

سَمِعْتُ أَبَا سَعِيدٍ الْخُدْرِيَّ يَقُولُ لاَ أُخْرِجُ أَبَدًا إِلاَّ صَاعًا إِنَّا كُنَّا نُخْرِجُ عَلَى عَهْدِ رَسُولِ اللَّهِ ﷺ صَاعَ تَمْرٍ أَوْ شَعِيرٍ أَوْ أَقِطٍ أَوْ زَبِيبٍ هَذَا حَدِيثُ يَحْيَى زَادَ سُفْيَانُ أَوْ صَاعًا مِنْ دَقِيقٍ قَالَ حَامِدٌ فَأَنْكَرُوا عَلَيْهِ فَتَرَكَهُ سُفْيَانُ