Musnad Ahmad 27:193

Yahya narrated to us, from Ubaydullah, Nafi’ informed me, from Abdullah ibn Umar, he said: The people of the Jahiliyyah used to sell the meat of the camel for the *habal al-habalah*. And *habal al-habalah* is: the she-camel gives birth to what is in her womb, then that which she gave birth to becomes pregnant. So the Messenger of Allah, peace and blessings of Allah be upon him, forbade them from that.