Bulugh al-Maram, Book 12, Hadith 1382 (English)

Shaddad bin Aus (RAA) narrated that the Messenger of Allah said: "Verily, Allah has prescribed proficiency in all things. Thus, if you kill, kill in the least painful manner you can; and when you slaughter an animal, do it in the best possible way; and any of you should sharpen his blade so that the animal may be spared from the suffering of the slaughtering."

وَعَنْ شَدَّادِ بْنِ أَوْسٍ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ " إِنَّ اَللَّهَ كَتَبَ اَلْإِحْسَانَ عَلَى كُلِّ شَيْءٍ, فَإِذَا قَتَلْتُمْ فَأَحْسِنُوا اَلْقِتْلَةَ, وَإِذَا ذَبَحْتُمْ فَأَحْسِنُوا اَلذِّبْحَةَ, وَلْيُحِدَّ أَحَدُكُمْ شَفْرَتَهُ, وَلْيُرِحْ (1756)‏ ذَبِيحَتَهُ" } رَوَاهُ مُسْلِمٌ (1757)‏.‏ ‏3 ‏- كذا "بالأصلين" ، وفي "الصحيح" : " فليرح".‏‏4 ‏- صحيح.‏ رواه مسلم ( 1955 )‏.‏

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also referenced under: Book 12, Hadith 1342 (In-Book)