" The first is having a hard heart. A man saw the Prophet kiss a baby and asked him, “Do you kiss your children?” The Prophet said, “Indeed, I do.” The man then said, “I have ten children, I never kissed any of them,” which was considered and aspect of the pride of being a tough Arab. To that the Prophet replied, “There is nothing in my religion for a man whose heart is void of mercy.” The Prophet also said, “Have mercy on those on the earth, and He who is in heaven will have mercy on you. "

― Hamza Yusuf , Purification of the Heart: Signs, Symptoms and Cures of the Spiritual Diseases of the Heart