Hazrat Umar (ra) sent Hazrat Utbah (ra) bin Ghazwan to Basrah to fight the people of Ubullah, who were from Persia. Whilst dispatching them, Hazrat Umar (ra) instructed them, “You and your companions shall continue along your path until you reach the borders of the Arab kingdom and the non-Arab lands. Go forth with the blessings and grace of God Almighty. Always fear God Almighty and remember that you are heading towards a fierce enemy.” Hazrat Umar (ra) then said, “I am confident that God Almighty will help you against them and I have written to Hazrat Alaa (ra) bin Hadrami for him to send Arfajah bin Harsamah along with you for assistance, for he is very experienced in fighting the enemy and well-versed in the art of war.” Hazrat Umar (ra) then stated, “Hence, you must take counsel from him and call the people unto God Almighty. Whoever accepts what you say, you are to accept their initiation into Islam, but whosoever rejects what you have to say, you shall impose the jizya (tax) upon them, which they ought to submit willingly. However, he who refuses to even pay that, then you are to use the sword.” That is to say, if they are not willing to pay the jizya whilst following their own religion and living there, and furthermore, if they are prepared to fight, then Hazrat Umar (ra) said that it is only then that they can take up the sword against them. Hazrat Umar (ra) then stated, “You must call all the Arabs you pass by to participate in the jihad and deal with the enemies very vigilantly and fear your Lord – Allah the Almighty.”
Hazrat Umar (ra) dispatched Hazrat Utbah (ra) to Basrah with 800 men and reinforcements were also sent later on. Hazrat Utbah (ra) conquered Ubullah, in which he then set the boundary of the city of Basrah. He is the first person to turn Basrah into a city and a settlement.
When Hazrat Umar (ra) bin Khattab appointed Hazrat Utbah (ra) as the governor of Basrah, he was residing in a place named Khareebah; this was an ancient city of Persia, which in Persian was known as وَھْشَتَابَاذْ اُرْدْشِیْر. The Arabs then named it Khareebah and the Battle of Jamal also took place nearby. Hazrat Utbah (ra) wrote a letter to Hazrat Umar (ra) explaining that such a land is necessary for the Muslims to remain in during the winter months and where they can rest whilst returning from battle. Hazrat Umar (ra) wrote back telling him that he should gather them in such a land which is close to water and grazing ground. In other words, if this is what they intended for, then it should be in a land where water is readily available and where there is grazing ground for the animals.
Thereafter, Hazrat Utbah (ra) settled the Muslims in Basrah where they constructed their buildings of bamboo. Hazrat Utbah (ra) built a mosque out of bamboo in 14 AH. He built the residence of the governor in an open space near the mosque. When the people would go forth to fight, they would dig up these houses of bamboo and tie them up as they departed, and when they would return, they would reconstruct the homes in the same manner. It was only later on that the people then built permanent houses. Hazrat Utbah (ra) gave the instructions to Mihjan bin Adrah who then laid the foundation stone of the Basrah mosque and had it built out of bamboo. Soon after Hazrat Utbah (ra) went to perform the Hajj, and appointed Mujashi‘ bin Mas‘ud as his deputy and entrusted him to leave for the Euphrates and handed the responsibility of leading the prayers to Hazrat Mughirah (ra) bin Shu‘bah.