That 'Ali used to slaughter two male sheep, one for the Prophet ﷺ and the other for himself. When this was mentioned to him, he said: "He ordered me to" - meaning the Prophet ﷺ - "So I will never leave it."  

عَنِ النَّبِيِّ ﷺ وَالآخَرُ عَنْ نَفْسِهِ فَقِيلَ لَهُ فَقَالَ أَمَرَنِي بِهِ يَعْنِي النَّبِيَّ ﷺ فَلاَ أَدَعُهُ أَبَدًا