The wikipedia entry about Battle of Mu'tah contains an unsourced assertion:
Khalid ibn Al-Walid reported that the fighting was so intense that he used nine swords which broke in the battle. Khalid, seeing that the situation was hopeless, prepared to withdraw. He continued to engage the Byzantines in skirmishes, but avoided pitched battle. It is said that Khalid killed at least one identified Arab Christian commander namely Malik.
But it doesn't provide any citation for the claim.
Is it true that Khalid said he broke nine swords in the battle of Mu'tah? What is the source of this information?