Battle of Firaz The Battle of Firaz was the last battle of the Muslim Arab commander Khalid ibn al - Walid in Mesopotamia ( Iraq ) against the combined forces of the Byzantine Roman Empire , Sassanid Persian Empire , and Christian Arabs . Khalid ' s force consisted of 15 , 000 men , while the combined forces of the Byzantine Empire , Sassanid Empire and Arab Christians were at least ten times larger than Khalid ' s army . The result of the battle was a victory for Khalid and the first Muslim conquest of Mesopotamia . The Muslim conquest of the Persian Empire was complete after their next victory at the Battle of al - Qādisiyyah . Background . By the end of 633 , the Muslims were the masters of the Euphrates valley . In this valley , Firaz at the outermost edge of the Persian Empire still had a Persian garrison . Khalid decided to drive away the Persians from this outpost as well fearing that the Persians would execute a well planned re - invasion of lost territory . He marched to Firaz with a Muslim force and arrived there in the first week of December 633 . Firaz was the frontier between the empires of Persia and Byzantium , and the garrisons of the Persians as well as the Byzantines were cantoned there . In the face of the Muslims , the Byzantine garrison decided to come to the aid of the Persian garrison . The united forces of the Persians , the Byzantines , and the Christian Arab auxiliary , were at least ten times the number of the Muslim force . Impressed by the imposing array of the coalition , the Byzantine general sent a haughty message to Khalid , demanding an unconditional surrender . Khalid replied that he would give reply on the battlefield . The battle . Khalid gave the enemy the option to cross the Euphrates . As soon as the enemy had crossed the Euphrates , Khalid commanded the Muslim force to go into action . The united forces of the Persians and the Byzantines had the river at their back , and the position was similar to that at the battle of Mazar . At Firaz , Khalid adopted the same tactics as he had adopted at Mazar . As the front ranks of both the forces committed themselves in the fighting , Khalid fixed his enemy on either flank with the help of his rear wings . Making a swift lightning movement , the Muslims dashed for the bridge on the river , and succeeded in occupying it . The enemy was thus held in a pincer movement . The Muslims intensified the attack and closed the noose round the neck of the enemy . In the mortal conflict that ensued , the enemy soon lost the ground . The withdrawing forces of the Persians and the Byzantines jumped into the river in a state of horror or confusion whilst the Muslim forces would shoot arrows at the retreating soldiers . It was a bloody battle , and over fifty thousand men from Byzantine , Persian and Arab Christian armies fell on the battleground . The battle was soon over and Firaz , the last stronghold of Persian Mesopotamia , fell to the Muslims . The battle of Firaz added further luster to the Muslim arms . Khalid ' s oath . In the beginning of the battle of Firaz when the odds appeared to be against the Muslims , Khalid undertook an oath that if he was victorious , he would undertake pilgrimage to Mecca , the House of God . After the victory of Firaz , Khalid stayed at Firaz for some days and made the necessary arrangements for the administration of the territory . In January 634 , while a garrison was kept at Firaz , orders were issued to the main Muslim army to return to Al - Hirah . Khalid stayed behind with the rear of the army . As the army moved forward on the road to Al Hirah , Khalid separated himself from the army , and took an unfrequented route to Mecca with a small escort . Khalid reached Mecca in time to perform the ' Hajj ' . After performing the pilgrimage secretly and fulfilling his vow , Khalid and his party rode back to Al Hirah . Before the last contingent of the main army from Firaz had entered Hirah , Khalid was also there , as if he had been all the time with the rear guard . Although Khalid had taken pains to ensure that he was not recognized at Mecca , news was nevertheless carried to Abu Bakr that leaving his charge in Iraq , Khalid had visited Mecca incognito . When Khalid reached Al Hirah , he got a letter from Abu Bakr asking him not to indulge in such adventure again .