What were the three incidents that occurred for the first time in the Battle of Mu'tah?

The Battle of Mu'tah was unique in ways that no other battle was. It was called a "ghazwah" (expedition) even though the Messenger of Allah, peace and blessings be upon him, did not participate in it. In it, he appointed three commanders in succession (Zayd ibn Harithah, then Ja'far, then 'Abdullah ibn Rawahah). Khalid ibn al-Walid took the banner after the death of the three commanders without being appointed by the Messenger of Allah, peace and blessings be upon him. The Prophet, peace and blessings be upon him, mourned the commanders before the news reached him, and he said: "Until the banner was taken by a sword from the swords of Allah, until Allah granted them victory."