‘It is narrated from Abdullah bin Yazid that Abu Ayash Zaid asked Sa’d (may Allah be pleased with him) about selling wheat with its husk removed in exchange for barley. So he (Sa’d) asked: Which of the two is superior? He replied: Wheat. So he (Sa’d) forbade it. And Sa’d (may Allah be pleased with him) stated that he heard the Messenger of Allah (peace and blessings of Allah be upon him) being asked about buying dry dates in exchange for fresh dates. So he (the Prophet) asked those sitting nearby:“Will the fresh dates decrease when they become dry? 1”The people said: Yes (they will decrease). So he forbade it. The author has narrated a similar hadith with chain «وكيع عن مالك» . Imam Tirmidhi says:
1- This hadith is Hasan Sahih,
2- The people of knowledge act upon this, and this is also the saying of Shafi’i and our companions.