It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade the sale of the unborn offspring of a pregnant animal. This type of sale was prevalent in the Age of Ignorance: a person would buy a camel/she-camel and set the payment term such that when the she-camel's unborn offspring would grow up and itself become pregnant, then he would pay the price.
Hadith Referenceالسنن المأثورة / باب في البيوع / 229
Hadith Takhrijصحیح بخاری، البيوع، باب بيع الغرر وحبل الحبلة، رقم: 2143، صحیح مسلم، البيوع، باب تحريم بيع حبل الحبلة، رقم: 1514