When the Holy Prophet migrated to Madina, there was a considerable number of Jews there. They were wealthy, and commanded great influence as they controlled all trade. The Holy Prophet laid down the policy of "Live and let live" with reference to the Jews. He accordingly entered into a treaty of mutual cooperation and collaboration with them. According to the terms of the treaty, the Jews were to enjoy religious freedom and there was to be no interference .in religious affairs. The Muslims and the Jews were to be on friendly terms, and were to help each other in the promotion of objects of common interest. It was stipulated that the Muslims and the Jews would jointly defend Madina against any enemy from. Without. The Jews were not to give protection to the Quraish of Makkah, and in the event of any attack by the Quraish, both the Muslims and the Jews were to join hands in the defense of the city.
"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