The Book of Transactions
وَحَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا عُبَيْدُ اللَّهِ، حَدَّثَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، عَنْ زَيْدِ بْنِ ثَابِتٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَخَّصَ فِي الْعَرَايَا أَنْ تُبَاعَ بِخَرْصِهَا كَيْلاً .Zaid b. Thabit (Allah be pleased with him) reported Allah's Messenger (ﷺ) granting concession in case of 'ariyya transactions and that implies selling of (dry dates for fresh dates) according to a measure
From Sahih Muslim, whose reports the scholars accept as authentic.