On the death of Umar, like the rest of Persia, Khurasan also revolted and broke away from the authority of the Muslims. Yazdjurd the Persian emperor made Merv his head quarters, and once again made preparations to measure swords with the Muslims and drive them out of Persia. Before Yazdjurd could lead the Persian forces against the Muslims, Yazdjurd fell a victim to the treachery and disloyalty of his own people, and he was killed in 651 C.F.
"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari