Yazdjurd crossed the Oxus and sought refuge with the Khaqan of Farghana. After the death of Umar, the Persians revolted against the Muslims and a greater part of Persia was lost to the Muslims. Availing of this opportunity, Yazdjurd with the help of a Turkish force reoccupied Merv.
"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