Abu Hurayrah reports: 'Whenever I see Hasan, my eyes are filled with tears because the Prophet (peace be upon him) went out one day and found me in the mosque. He took me by the hand and I walked with him. He did not speak to me until we reached the Qaynuqa market. He walked there and looked around then he left and I went with him until we returned to the mosque He sat and wrapped himself in his garment. He asked: "Where is the little one? Call me the little one". Hasan came running until he fell in the Prophet's lap, and put his hand in the Prophet's beard. The Prophet opened his mouth and Hasan's mouth touched the Prophet's mouth. The Prophet then said: "My Lord! Love him and love anyone who loves him".' [Bukhari]
Here the reporter, Abu Hurayrah, says that his eyes were tearful whenever he saw Hasan, the Prophet's grandson, because he would remember this event. The hadith draws a very normal picture of a grandfather wanting to play with his little grandson. He allows the child to play with his beard and he lovingly puts his mouth over the child's mouth. But the prayer he says is exceptionally moving. He prayed to God not only to love the child but to love those who love him as well. And history records that all Muslims loved the Prophet's grandsons. He not only merited this love on account of his relation to the Prophet, but he was a man people liked and wished to associate with. Moreover, when he became Caliph, he stepped down after six months, to ensure the unity of the Muslim state.
"Al-Adab al-Mufrad with Full Commentary: A Perfect Code of Manners and Morality