From Sahih Bukhari (Hadith 3843):
Narrated Ibn `Umar:In the pre-Islamic period of ignorance the people used to bargain with the meat of camels on the principle of Habal-al-Habala which meant the sale of a she-camel that would be born by a she-camel that had not yet been born. The Prophet (ﷺ) forbade them such a transaction
Reference: Bukhari 3843