سنن النسائي

It was narrated that Rafi bin Khadij said: "I said: 'O Messenger of Allah we are going to meet the enemy tomorrow and we do not have any knives.' The Messenger of Allah (ﷺ) said: "If the blood is shed and the name of Allah is mentioned, then eat, unless (it is slaughtered (with teeth or nails, and I will tell you about that. As for teeth, they are bones, and as for nails, they are the knives of the Ethiopians."' (Sahih )