Seestan the eastern province of Persia, and the home of the legendary hero Rustam of Shahnama fame was conquered by the Muslim forces sent to Seestan. The Muslim advance had been obstructed by the Persian forces at the frontier. After a violent fight the Persian forces had been repulsed. The Muslims had thereafter advanced to Zaranj the capital of the province which fell after a prolonged siege. Thereafter the Muslims suppressed all opposition, and became the masters of the entire province.
"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