Riyad as-Salihin

Abu Ya'la Shaddad bin 'Aus (May Allah be pleased with him) reported: Messenger of Allah (ﷺ) said, "Verily Allah has prescribed Ihsan (kindness) for everything. So when you kill, you must make the killing in the best manner; when you slaughter, make your slaughter in the best manner. Let one of you sharpen his knife and give ease to his animal (in order to reduce his pain)."

[Muslim].