Musnad Abu Ya'la al-Mawsili 49:10

Ali ibn al-Ja'd narrated to us, Abd al-Rahman ibn Abd Allah ibn Dinar informed us, from Zayd ibn Aslam, from Abu Waqid al-Laythi, who said: The Messenger of Allah (may Allah bless him and grant him peace) arrived in Medina, and the people were cutting the humps of camels and cutting the fat-tails of sheep. The Messenger of Allah (may Allah bless him and grant him peace) said: "Whatever is cut from an animal while it is alive, it is dead (i.e., carrion)."