(21) The Book of Transactions
كتاب البيوع
(14) Chapter: The prohibition of selling fresh dates in exchange for dry dates except in the case of 'Araya
(14) باب تَحْرِيمِ بَيْعِ الرُّطَبِ بِالتَّمْرِ إِلاَّ فِي الْعَرَايَا ‏‏
Sahih Muslim 1539 i 

Ubaidullah reported this hadith with a slight change of words on the same authority (as quoted above).

وَحَدَّثَنَاهُ ابْنُ الْمُثَنَّى، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ عُبَيْدِ اللَّهِ، بِهَذَا الإِسْنَادِ وَقَالَ أَنْ تُؤْخَذَ بِخَرْصِهَا ‏.‏
Reference : Sahih Muslim 1539i
In-book reference : Book 21, Hadith 84
USC-MSA web (English) reference : Book 10, Hadith 3685
  (deprecated numbering scheme)