From Sahih Muslim (Hadith 3805):
Abu Huraira (Allah be pleased with him) reported:Two types of trarisactions have been forbidden (by the Holy Prophet), al-Mlulamasa and al-Munabadha. As far as Mulamasa transaction is concerned, it is that every one of them (the parties entering into transaction) should touch the garment of the other without careful consideration, and al-Munabadha is that every one of them should throw his cloth to the other and one of them should not see the cloth of his friend
Reference: Muslim 3805