Why didn't the Messenger, may Allah bless him and grant him peace, participate in the Battle of Mu'tah himself?

There is no known reason for the Prophet, peace and blessings be upon him, being absent specifically from the Battle of Mu'tah. However, he did stay behind from some battles out of compassion and pity for his Companions, as he did not find enough mounts to carry all the Companions who did not wish to stay behind from him, and it might be difficult for them to bear their own expenses and travel, as indicated by the hadith of Abu Hurayrah in Sahih Muslim. The Prophet, peace and blessings be upon him, personally led the greatest battles, and sent detachments and his Companions for dawah (inviting to Islam) or to fight enemies in different places. The Battle of Mu'tah occurred because of the killing of Al-Harith ibn Umayr Al-Azdi, the messenger of the Prophet, peace and blessings be upon him, to the king of Busra.