Yahya bin Husain narrates from his grandmother that I heard the Prophet (peace be upon him) say three times: "May Allah's mercy descend upon those who shave their heads." The third time, people requested that those who shorten their hair be included in the supplication as well, so the Prophet (peace be upon him) included them too. And I heard the Prophet (peace be upon him) say: "If even a slave is appointed over you, who leads you according to the Book of Allah, then listen to him and obey him."