Ali book Nahj al-Balagha
Variant translation:
Awaken your heart to kindness and mercy for the people and love and tenderness for them. Never, never act with them like a predatory beast which seeks to be satiated by devouring them, for the people fall into two categories: they are either your brethren in faith or your kindred in creation.
Nahj al-Balagha, Letter 53: An order to Malik Al-Ashtar