The Roman army, with 10,000 soliders, outnumbered the Muslims 3:1 at the Battle of Mutah. Some of the Muslims feared the large army and wanted to retreat, but the senior companions bolstered their courage.
Prophet Muhammad had appointed a leader for the army, with two backup leaders in case the first one was martyred.
This was a hard battle. Jaffer ibn Abi Talib was the first leader, and he was martyred in the battle. Zayd ibn Haritha was the second leader, and he also became martyred. Abdullah ibn Rawaha was the final designated leader, and fell as well. Overall, about 11 Muslims were martyred in the battle, and the Muslims eventually ended up retreating.
Back in Medina, the prophet was witnessing the battle through his ilm ul ghayb (knowledge of the unseen) and narrated the battle in realtime, both the heroics and the shahadats.
The final verdict on the battle is mixed. Some historians called it a defeat since the Muslims retreated, others call it a draw due to the insignificant numer of casualties, where neither side took over the other's land, and some historians called it a strategic victory since fighting a non-arab army put htem on the map on a global stage and gave them experience to fighting non-arab armies.
Lecture notes available at http://www.why-quran.org/?p=665.
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