Musnad Abu Ya'la al-Mawsili 6:137

Zuhayr narrated to us, Abd al-Rahman ibn Mahdi narrated to us, from Malik, from Abdullah ibn Yazid, from Abu Ayyash, that Sa’d was asked about [the exchange of] white wheat for barley, and he disliked it. He said: I heard the Messenger of Allah (may Allah bless him and grant him peace) being asked about fresh dates for dried dates. He said: "Do fresh dates decrease when they dry?" They said: "Yes." He said: "Then do not [do it]."