Musnad Ahmad 27:150

Sufyan narrated to us, Ayyub—meaning Ibn Musa—narrated to us, from Nafi', who said: I heard a man from Banu Salama narrating to Ibn Umar: "A slave girl of Ka'b ibn Malik was grazing sheep of his at Sal'. Death reached one of them, so she took a sharp stone and slaughtered it with it. He [Ka'b] then ordered it to be eaten."