The Prophet ﷺ forbade the sale of the unborn offspring of an unborn animal. He explained that this means a she-camel gives birth to her young, and then that newborn female itself becomes pregnant.
حدثنا أحمد بن حنبل حدثنا يحيى عن عبيد الله عن نافع عن ابن عمر عن النبي ﷺ نحوه وقال وحبل الحبلة أن تنتج الناقة بطنها ثم تحمل التي نتجت
Bukhari narrated it in the Book of the Virtues of the Ansar, Chapter on the Days of Jahiliyyah, no. 3843, and Muslim in the Book of Sales, Chapter on the Prohibition of Selling the Unborn Offspring of an Unborn Animal, no. 1514, from the hadith of Yahya Qattan through this same chain, and it is also in Musnad Ahmad, 2/15.