Ten years later, when Abdullah b Sa'ad was the governor, the Muslim forces invaded Nubia for the second time. The Muslim forces advanced into Nubia, and besieged Dongola the capital of Nubia. Here history repeated itself. The Nubian archers known as the "Archers of the Eye" let loose a shower of arrows aimed at the eyes of the Muslim warriors. The Nubians were expert marksmen, and their arrows caused a good deal of consternation among the Muslim ranks.
As the Muslims were not able to overpower the Nubians, they accepted the Nubian offer of peace. According to the treaty that was signed, each side agreed not to make any aggression against the other. Each side agreed to afford free passage to the other party through its territories. Nubia agreed to provide 360 slaves to Egypt every year, while Egypt agreed to supply grain to Nubia according to demand.
"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