Yahya related to me from Malik from Zayd ibn Aslam that Ata ibnYasar said, "The Messenger of Allah, may Allah bless him and grant himpeace, said, 'Dried dates for dried dates is like for like.' It wassaid to him, 'Your agent in Khaybar takes one sa for two.' TheMessenger of Allah, may Allah bless him and grant him peace, said,'all him to me.' So he was called for. The Messenger of Allah, mayAllah bless him and grant him peace, asked, 'Do you take one sa fortwo?' He replied, 'Messengerof Allah! Why should they sell me gooddates for assorted low quality dates, sa for sa!' The Messenger ofAllah, may Allah bless him and grant him peace, said, 'Sell theassorted ones for dirhams, and then buy the good ones with thosedirhams.' "
USC-MSA web (English) reference: Book 31, Hadith 20
Arabic reference: Book 31, Hadith 1313