I asked, "Did you used to take out the fifth from food during the time of the Messenger of Allah ﷺ?"He replied, "We obtained food on the day of Khaybar, and a man would come and take from it the amount that was enough for him, then leave."
حدثنا محمد بن العلاء حدثنا أبو معاوية حدثنا أبو إسحق الشيباني عن محمد بن أبي مجالد
قلت هل كنتم تخمسون يعني الطعام في عهد رسول الله ﷺ فقال أصبنا طعاما يوم خيبر فكان الرجل يجيء فيأخذ منه مقدار ما يكفيه ثم ينصرف
Its isnad is sahih. Ahmad narrated it, 4/354, from the hadith of Abu Ishaq Shaybani through this route. Ibn Jarud graded it sahih, no. 1072, and Hakim graded it according to the standard of Bukhari, 2/126, and Dhahabi agreed with him.