كتاب البيوع
Read the English translation first, with the original Arabic directly underneath.
it was narrated that Sa'd said:
"The Messenger of Allah was asked about (buying) fresh dates with dried dates, and he said to those who were around him: 'Will fresh dates decrease (in weight or volume) when they dry out?" they said Yes,' so he forbade that."
أَيَنْقُصُ الرُّطَبُ إِذَا يَبِسَ