After gaining victory over Qadisiyyah, the Muslim army was then granted victory in Babylon, which is an ancient city of modern-day Iraq and which has been mentioned by the Holy Quran in relation to Harut and Marut. This place was where Kufa is now situated. This is what has been mentioned in the introduction for the names of the cities. It is further written that they reached the historical city of Kusa, which is where Nimrod imprisoned Hazrat Abraham (as). The prison was still intact at that time. When Hazrat Sa‘d (ra) reached that place and saw the prison, he recited the following verse of the Holy Quran:
تِلْکَ الْاَیَّامُ نُدَاوِلُہَا بَیْنَ النَّاسِ
“And such days We cause to alternate among men [that they may be admonished].” (Surah al-e-Imran, Ch.3: V.141)
As they journeyed further from Kusa, they reached a place named Bahra Sheer. According to Mu‘jam-ul-Buldan, which also explains the names of the cities, the name of this place was Bahuri Seer, situated to the west of the Tigris River, near the Iraqi city of Midian, and in the outskirts of Baghdad. This is where the hunting lion of Chosroes was kept.
So when the army of Hazrat Sa‘d (ra) had reached close by, this beast was unleashed upon them. With its thunderous growl, the lion launched its attack upon the army. Hashim bin Abi Waqas (ra), the brother of Hazrat Sa‘d (ra) who was the commander of the frontline, struck the lion in such a manner that it collapsed on the spot. The Battle of Midian also took place during this expedition. Midian was the headquarters of Chosroes where his white palaces were located. Between the Muslims and Midian was the Tigris River. The Iranians had completely destroyed the bridge of the river. Hazrat Sa‘d (ra) then said, “O Muslims, the enemy has taken refuge with the river, so let us now swim across the river.” Having said this, Hazrat Sa‘d (ra) led the horse in the river and the soldiers followed their commander by also taking their horses in the river and in this way, the army of the Muslims crossed the river. Having witnessed these extraordinary scenes, the Iranians began wailing with fear and fled immediately thinking some spirits had come. As the Muslims advanced, they took control of the city and the palaces of Chosroes and in this way, the prophecy of the Holy Prophet (sa) came to fulfilment. This [prophecy] was revealed to the Holy Prophet (sa) as he struck the boulder with the pickaxe whilst digging the ditch prior to the Battle of the Ditch, when he said, “I have been shown the white palaces of Midian falling.” Hence, having seen these palaces in a derelict state, Hazrat Sa‘d (ra) recited the following verses of Surah al-Dukhan:
كَمْ تَرَکُوْا مِنْ جَنّٰتٍ وَّ عُیُوْنٍ۔ وَّ زُرُوْعٍ وَّ مَقَامٍ کَرِیْمٍ۔ وَّ نَعْمَۃٍ کَانُوْا فِیْہَا فٰکِہِیْنَ۔ کَذٰلِکَ وَ اَوْرَثْنٰہَا قَوْمًا اٰخَرِیْنَ
“How many were the gardens and the springs that they left behind! And the cornfields and the noble places! And the comforts wherein they took delight! Thus [it was destined to be]. And We made another people inherit these things.” (Surah al-Dukhan, Ch.44: V.26-29)
Thereafter, Hazrat Sa‘d (ra) wrote to Hazrat Umar (ra) seeking permission to advance further, to which Hazrat Umar (ra) replied that he should suffice with what was at hand and attention should be given to establishing law and order in the conquered lands. Hence, by establishing Midian as the headquarters, Hazrat Sa‘d (ra) began his efforts to strengthen the administration and he carried this out in an excellent manner.