After the battle of Jalaula and Ahwaz, Umar had ordered that there was to be no further advance in Persia. The orders of Umar were that the Muslims could advance as far as the land route could carry but where some sea or body of water intervened that was not to be crossed.
When the Muslims overran Iraq, and won the battles of Qadisiyya, Ctesiphon, Jalaula, and Ahwaz the spirits of the Muslims ran high and they dreamt of conquering distant lands.
At this time Ula b. Al Hadrami was the Governor of Bahrein. He had led the apostasy campaign in Bahrain and had succeeded in restoring law and order. Between Bahrain and Persia lay the Persian Gulf and across the Persian Gulf was the Persian province of Fars which could boast of such cities as Persepolis and Shiraz.
Anxious to win glory in the name of Islam, Ula called the local Arabs to arms. The response was encouraging, and Ula mustered a considerable force. Ula thought that with this force he could easily capture a greater part of Fars.
He was aware of the command of Umar that no further advance in Iran should be undertaken. Ula knew that if he sought permission from Umar to undertake an expedition against Fars such permission would not be forthcoming. He thought that the best course would be to launch the attack, and when the Caliph would hear of his success he would approve the fait accompli.
Thus notwithstanding the ban imposed by Umar, Ula ordered a march to Fars. The force was divided into three columns, and placed under the command of Jarud b. Mualla; Sawwar b. Hamam: and Khuleid b. Mundhir. The Muslim forces were transported by boats across the Persian Gulf, and they landed on the eastern coast of the Persian Gulf.
The Muslim forces then started the march inland towards Shiraz and Persepolis. Half way at Tawoos they found their way barred by a sizable Persian force.
Both the sides deployed their forces for battle. The contest was violent. There were heavy casualties among the Persians, but the Muslims also suffered heavily. The two Muslim commanders Sawwar and Jarud fell fighting. The command was then taken over by Khuleid. He launched a counter attack against the Persians and after putting up a gallant fight, the Persians withdrew.
As Khuleid surveyed the position he felt that unless he was strongly reinforced further advance in Fars was not possible. He accordingly decided to return to the sea shore and await further reinforcements.
When the Muslims came to the shore of the Persian Gulf, they found that by a flanking movement the Persians had already burnt the boats by which the Muslims had crossed the Persian Gulf.
The Muslims now found themselves in a precarious situation. They were not strong enongh to march inland to Fars. With the burning of the boats they could not recross to Bahrain. The only alternative was to march along the east coast of the Persian Gulf to Ahwaz and then to Basra.
After a day's march the Muslims reached the town of Jannaveh, and here they found that their way was blocked by a large Persian force led by Shahrak the Governor of Fars. The Persian force was too large for the Muslims to attack. The Muslims accordingly went into camp and prepared for a defensive action.
Shahrak launched several attacks against the Muslims but he was not able to make any headway. He accordingly withheld further attacks, and decided to blockade the Muslims. In the meantime the commander of the stranded Muslim force managed to send a messenger to Umar. When Umar came to know that the campaign had been launched without his permission and that it had failed he felt very angry and unhappy. He, however, decided to take immediate action to relieve the stranded army.
Umar wrote to Utba bin Ghazwan the Governor of Basra to send a force to the relief of the Muslims stranded in Fars. Utba sent a large force led by Asim b. Amr, and Abu Sabra b. Abi Ruhm. It moved along the coastal route. In the meantime Shahrak also got some reinforcement, and he was planning thc assault of the Muslim camp. The Muslim relief force arrived at the nick of the time and that turned the balance in favour of the Muslims. In the confrontation that followed the Persians were defeated, and they took to flight after heavy losses. The Muslim forces marched back to Basra. That was the end of the campaign in Fars. It cost Ula b. Hazrami his governorship, from which office he was removed.