Al Mamoun then sent for Tahir, and named him governor of Khorassan on the spot; he made him also a present of an eunuch, to whom he had just given orders to poison his new master if he remarked anything suspicious in his conduct. When Tahir was solidly established in his government he ceased mentioning Al Mamoun's name in the public prayers as the reigning Caliph. A dispatch was immediately sent off by express to inform Al Mamoun of the circumstance, and the next morning Tahir was found dead in his bed. It is said that the eunuch administered the poison to him in some sauce. Al Mamoun placed his two sons under the tuition of Al Farra, so that they might be instructed in grammar. One day Al Farra rose to leave the house, and the two young princes hastened to bring his shoes. They struggled between themselves for the honor of offering them to him, and they finally agreed that each of them should present him with one slipper. As Al Mamoun had secret agents who informed him of everything that passed, he learned what had taken place, and caused Al Farra to be brought before him. When he entered, the Caliph said to him: "Who is the most honored of men?" Al Farra answered: "I know not any one more honored than the Commander of the Faithful." "Nay," replied Al Mamoun, "it is he who arose to go out, and the two designated successors of the Commander of the Faithful contended for the honor of presenting him his slippers, and at length agreed that each of them should offer him one." Al Farra answered: "Commander of the Faithful, I should have prevented them from doing so had I not been apprehensive of discouraging their minds in the pursuit of that excellence to which they ardently aspire. We know by tradition that Ibn Abbas held the stirrups of Hasan and Husain, when they were getting on horseback after paying him a visit. One of those who were present said to him: 'How is it that you hold the stirrups of these striplings, you who are their elder?' To which he replied: 'Ignorant man! No one can appreciate the merit of people of merit except a man of merit.'" Al Mamoun then said to him: "Had you prevented them, I should have declared you in fault. That which they have done is no debasement of their dignity; on the contrary, it exalts their merit. No man, though great in rank, can be dispensed from three obligations: he must respect his sovereign, venerate his father, and honor his preceptor. As a reward for their conduct, I bestow upon them twenty thousand dinars ($50,000), and on you for the good education you give them, ten thousand dirhems" ($2,500).