In the eighth year after Hijrah, Mecca was conquered by Allah’s Messenger. The House of Allah was purified from the filth of idols with `Ali’s idol-breaking act. Allah’s Messenger sent groups to propagate Islam and to invite people to monotheism. He did not declare war.
One of these persons was Khalid ibn Walid who was dispatched not as fighter but as propagator. On his way Khalid came to a tribe one of whom had killed his uncle in the pre-Islamic era and had looted whatever belonged to him. When Khalid was alight near the water sources of Banu-Judhaymah, they took arms. Khalid said, “Put aside your arms, for people have become Muslims.” He had their hands tied and killed whomever he wished.
When the news came to Allah’s Messenger, he raised his hands saying, “O Lord! I seek immunity from what Khalid has done!” Then, the Holy Prophet sent `Ali with money to look into their affairs. `Ali gave them back whatever Khalid had taken from them. He paid the blood money for all and the extra money which `Ali had with him was paid to them by the command of the Holy Prophet.
When `Ali came back, the Holy Prophet said that what he had done was good and right. On the words of Ya`qubi, the Holy Prophet said, “What you have done is better than the red camels.” It was at this time addressing `Ali, Allah’s Messenger said, “May my father and mother be your ransom.” (Al-Sirah al-Nabawiyyah: 430/2 )