After the victory of Khaybar, the power of Islam and the authority of the Prophet (may Allah bless him and grant him peace) increased so much that he sent letters to various kings and invited them to Islam. The letters were sent to the Sultan of Byzantine, to the King of Iran, Najashi - the King of Abyssinia and to the Emperor of Egypt.

In the neighbouring area of Arabia was a king who ruled under the influence of the Byzantine Empire. His name was Harith bin Abi Shamir. He enjoyed the authority of a king and was conceived as such by the commonality. The Prophet (may Allah bless him and grant him peace) dictated a letter in his name and giving it to his special emissary, Harith bin Umair, directed him to deliver the letter to the king and return with his reply.

When the Prophet’s (may Allah bless him and grant him peace) emissary entered the domains of Harith bin Abi Shamir, one of his guards at the frontiers arrested him and put him to death. This incident fell hard upon the Muslims and they were deeply angered by his death. An emissary was sanctioned protection by all the nations of the world.

The Prophet (may Allah bless him and grant him peace) sent a message to Harith bin Abi Shamir, "A worker of yours, Sharjeel bin Umroah, has put an innocent person to death who was coming to you just to deliver a letter. The person was alone and unarmed in your territories and his journey was not to express any enmity, even then, he was put to death. To kill an ambassador is not permissible in any tribe, nation or religion. As your officer has murdered Harith bin Umair, it should be made known whether he has wilfully done the deed, or by your approval and orders? If he has killed our ambassador without your approval, you must hand over the person to us so that he could be sentenced for his deed, but if your approval was also included in this crime, then you are also responsible for this murder and you should better be prepared for the punishment as well".

Harith bin Shamir replied in the letter, "I am an autonomous ruler of my country, and the decision rests with me whom to kill or absolve. None has the right for my accountability. It should be clear that the ambassador was put to death at my orders".

When the Prophet (may Allah bless him and grant him peace) received such an irresponsible and insolent reply, he at once decided to chastise Harith bin Abi Shamir, and sent an army of three thousand soldiers into his domains - Ghassan. Coincidentally, the king of Asia-Minor was thinking of invading Iran. He had gathered an army of one hundred thousand veteran soldiers. On request of Harith bin Shamir this army came to his help. It is not known how many men Harith himself had. Some historians have given the number of ten thousand soldiers.

Islamic army faced these forces at a place called "Mutah". This area was in the dominions of Ghassan. When the Islamic army left Madinah, the Prophet (may Allah bless him and grant him peace) assigned its command to his foster son ZaydR.A bin Harith.

One hundred thousand Roman soldiers, sent by the Roman king were armed to teeth with war equipment. They were also skilled at various war methodologies. They formulated contingents of six thousand soldiers, each called a "Legion". The Legion was divided into thirty groups, each of which was called "Manipool". Each Manipool consisted of two hundred soldiers. This was further subdivided into two groups each with one hundred soldiers and was called "Century". All the Roman soldiers wore steel helmets and armour. Their shields were large and their spears and swords extraordinarily long. They were also familiar with the formation of flanks.

When the small Muslim army came face to face with the Romans, some Muslims said that they should first assess their chances of victory before indulging in the fight. Although the enemy had always out numbered them in previous battles but this time the enemy before them was forty or fifty times in comparison. It was also equipped with armoury of highest quality and of new style. Whereas some Muslim soldiers lacked even basic armour and weapon.

The commander of the Islamic army, ZaydR.A bin Harith zealously said, "We have come to fight in the way of Allah, if we kill the enemy for victory, Paradise is our reward. The same is ours if we die and are defeated. Only those fear the enemy numbers who lack Faith in the hereafter. Why should we be afraid of the numbers of the enemy?" These words of ZaydR.A bin Harith induced rejuvenation among the Muslims and they became prepared for the battle.

Before the battle commenced, the Muslims adopted the same strategy as employed in earlier battles. They arranged themselves in Flanks. This time expected results were not obtained by this formation, because the Romans also knew this skill. Furthermore, their armoury was far superior and advanced to that of the Muslims. They were also well trained in throwing spears.

ZaydR.A bin Harith died in the early moments of battle. His command was replaced by Ja’far bin Abi Talib. He continually used sword and issued instructions to the army. Under his command, the Islamic army while engaged in fighting reached Mutah. At this place Ja’far bin Abi Talib was martyred. He had fought the entire battle valiantly. Even when both his hands had been cut off, he kept on fighting with the help of his legs, till he breathed his last.

After Ja’far bin Abi Talib’s death, Abdullah bin Rawaha, who belonged to the Ansar was appointed the commander of the Muslim army. To encourage and motivate soldiers, Abdullah bin Rawaha began reciting the Holy Quranic verses. He was reciting verses about Jihad and entrance into Paradise. He was also using his sword fiercely and warning the Muslims to maintain their lines and face the enemy with complete unity.

Had the Muslims not maintained their formation in this battle at Mutah, all would have been killed. It was only their unity in maintaining flanks that led them to consistently face the far stronger and more powerful enemy till evening.

Abdullah bin Rawaha was also martyred in this battle and Khalid bin Walid took over the charge. Some traditions say that this battle ended in a single day. Two factors allowed the Muslims to remain unbent till evening. One was Khalid bin Walid’s unparalleled leadership and military proficiency and the other was the darkness of night. In those days, battles aborted automatically at dark.

Before taking over the command of the Muslim army, Khalid bin Walid was leading a contingent of five hundred soldiers. His unmatched strength could be estimated by the fact that from the start of the battle till end, nine strong swords were broken by his hands. He changed his sword nine times. On taking over the command, he re-organised the Muslim troops and ordered them to launch a continuous attack on the enemy.

Till then three out of six Muslim contingents had been completely finished with fifteen hundred Muslim soldiers martyred. After the reorganisation of the remaining army Khalid bin Walid launched a lightening attack and advanced swiftly. In his first attack, he killed the commander-in-chief of the enemy. His name was Malik bin Albaladi. This attack by Khalid bin Walid was so intense and sudden that Harith bin Shamir and his allied Roman army lost its courage. They thought that the Muslims had received fresh reinforcements. They began to recede when the darkness of night started to prevail. Khalid bin Walid also left for Madinah along with the remaining army.

In this battle the Muslims lost two thousand lives. Nearly seventy per cent of the Muslim army was martyred. Among the martyrs were two very venerated personalities, Ja’far bin Abi Talib who grew up with the Prophet (may Allah bless him and grant him peace) and was considered his foster brother and ZaydR.A bin Harith who was a freed slave and the Prophet (may Allah bless him and grant him peace)’s adopted son. ZaydR.A bin Harith was among the first four Muslims to enter Faith.

It was due to his exemplary valour and military expertise that Khalid bin Walid safely delivered one thousand soldiers out of danger and reached Madinah. For this reason, the Prophet (may Allah bless him and grant him peace) honoured him by the title of "Saif Ullah" (the sword of Allah). Apart from the outcome of the Battle of Mutah, the Muslims received successive victories in the land of Hajjaz and flags of their victories were hoisted everywhere. In those days whosoever held his hold on Hajjaz could rule over the whole of Arabia. The Prophet (may Allah bless him and grant him peace) turned all the tribes of Hajjaz to Islam.