After the conquest of Tustar it was found that some Persian soldiers from the army of Hormuzan had escaped to Sus, and there they had collected under the command of Shahryar, a brother of Hormuzan.
After settling the affairs at Tustar, Abu Musa left a garrison there and with the rest of the army marched to Sus. Sus lay to the north west of Tustar. Like Tustar, Sus was also a walled city. When the Muslim forces reached Sus some time in January 641, the Persians shut the gates of the city, and remained on the defensive. The Muslims set up posts around the city and tightened up the arrangements for the siege.
The Persians made occasional sallies to break through the Muslim lines, but they were driven back to the city. The Muslims made attacks to break through the gates of the city, but failed to achieve their object.
One day a Persian priest appeared on the wall of the city , and addressing the Muslims said:
"O Arabs we know from the prophesies in our holy books that Sus will not be taken except by Dajjal, or by a people among whom there is a Dajjal. If you have Dajjal among you, you will conquer us; if not, do not bother to besiege us.
Abu Musa brushed away this prophesy as a superstition. Siyah the Persian General who had crossed over to the Muslim camp at Ahwaz told Abu Musa that as he had abjured the Persian faith, he was the Dajjal in Persian terminology, and as he was in the midst of the Muslims, they were destined to conquer Sus. Siyah said to Abu Musa:
"Leave the capture of Sus to me. I will do so through a stratagem of which Dajjal alone could be capable." Abu Musa let Siyah have his way.
The following day when the Persian priest Once again appeared on the walls of the city, and wanted to know whether any Dajjal was there, Siyah responded to the call and said that Dajjal was very much there and as such the state of Sus was sealed. When the Persians came to know that a Dajjal had appeared outside their city they were demoralised, and felt that under the circumstances any further resistance was futile.
One day as the first light of dawn appeared the Persian sentries on the wall by the main gate saw a Persian officer with his uniform stained with blood lying on the ground near the gate. There had been fighting at this spot the previous night, and the Persian soldiers thought that a wounded Persian officer had lain there all the night. The Persian soldiers rushed to the aid of the wounded Persian officer. They opened the gate and carried a bed to lift the wounded officer.
As the Persian soldiers approached the wounded officer, he sprang to his feet, and falling upon the soldiers with the speed of lightning killed all of them. This hero was Siyah, the Dajjal. The Muslim soldiers lurked near the gate, and as soon as the gate was opened and the sentries had been killed the Muslims led by Siyah rushed forward in the city carrying havoc. Siyah shouted at the top of his voice:
"O ye Persians, surrender, for the Dajjal has come."
The Persians taken by surprise rallied in a desperate bid to measure swords with the advancing Muslims. The Persians, however, fell back. Soon word went from house to house in the city "Dajjal of whom our holy books prophesied has appeared." As the sun rose, more Muslim forces rushed in through the gates, and the Persian resistance broke down. The Persians surrendered. Thanks to the genius of Siyah, the historic city of Sus was conquered by the Muslims. Turning to Siyah, Abu Musa said:
"O one eyed one; you and your comrades are not as we thought you were." Siyah accepted the compliment.
Abu Musa reported the conquest of Sus to Umar. In his despatch, Abu Musa referred to the prophesy about Dajjal and the role that Siyah had played as Dajjal. Abu Musa also reported that in one of the temples of Sus they had come across the coffin of the Prophet Daniel. Considerable booty was captured at Sus, and the usual one-fifth share of the booty was sent to Madina. The rest was distributed among the soldiers on the spot.
Umar appreciated the services of Siyah and his comrades and desired that their pay should be doubled. Umar also desired that the remains of the Prophet Daniel should be buried with due ceremony. Siyah and his comrades felt happy at the recognition of their services by the Caliph of Islam. In compliance with the orders of Umar, Abu Musa arranged for the burial of the remains of the Prophet Daniel. Abu Musa himself led the funeral prayer, and the remains of the Prophet Daniel who had died sonme 13,00 years earlier were buried by the side of the river.