Narrated Ibn 'Umar: In the pre-lslamic period of ignorance the people used to bargain with the meat of camels on the principle of Habal-alHabala which meant the sale of a she-camel that would be born by a she-camel that had not yet been born. The Prophet forbade them such a transaction.
— Sahih Bukhari, Volume 5, Book 58: Merits of the Helpers in Madinah (Ansaar), Hadith #183