Having destroyed the idols of the Kaaba, the Holy Prophet sent out small expeditions to the neighboring settlements to destroy the idols in the local temples. There after a number of expeditions were sent to the neighboring tribes to call them to Islam. The Holy Prophet issued instructions that the tribes who accepted the call were not to be harmed. Khalid b Walid was sent to the tribe of Banu Jazima. The tribe accepted the call and declared themselves as Muslims, but Khalid b Walid who had an old feud with the tribe asked the men to lay down arms and then had them killed. When the Holy Prophet came to know of this he felt much annoyed. He raised his hands towards heaven and said "O Lord I am not responsible for what Khalid has done." The Holy Prophet sent Ali with a good deal of money to smooth the feelings of Banu Jazima. Ali paid indemnity for the blood that had been shed. He treated them generously, expressed great regrets at what had happened and assured them of the good will of the Muslims. Ali lived in the midst of the tribe for some time, and educated them in the Islamic way of life. Ali performed the mission entrusted to him with great credit, and returned to Makkah when the Banu Jazima were fully satisfied.
"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