Hussain Kamani – 40 Ahadith of Imam An-Nawawi 17 – Striving For Excellence

On the authority of Abu Yaala Shaddad bin Aws (r), that the Messenger of Allah (s) said:
Verily Allah has prescribed ihsan (proficiency, perfection) in all things. So if you kill then kill well; and if you slaughter, then slaughter well. Let each one of you sharpen his blade and let him spare suffering to the animal he slaughters. [Muslim]