The Book of Transactions (Kitab Al-Buyu`)
Muslim :: Book 10 : Hadith 3612
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.