Musnad Ahmad 27:1412

Qutaybah ibn Sa'id narrated to us, Ibn Lahi'ah narrated to us, from 'Uqayl, from Ibn Shihab, from Salim ibn 'Abdullah, from his father: "That the Messenger of Allah (ﷺ) commanded that the blades be sharpened, and that they be hidden from the animals, and if one of you slaughters, let him do it quickly."