Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "For the young in the womb (of an animal), the slaughter of its mother counts as the slaughter of that young, provided it has grown hair."
Al-Tabarani recorded it in al-Mu'jam al-Awsat and in al-Mu'jam al-Saghir. He did not record the words "provided it has grown hair." Its chain contains Ibn Ishaq, who is thiqah (trustworthy) but a mudallis (one who conceals defects in the chain); the remaining narrators of al-Mu'jam al-Awsat are thiqat (trustworthy).