The Chachnāma (Fatḥnāma-yi Sind) 18: The army marches to Siwistan.

18

From that place he went to Siwistan, and when he approached it, Matta, its chief, came forth with great alarm and a large retinue to meet him. A battle was fought, Chach was victorious, and Matta, with his army, fled and took refuge in the fort. Chach besieged it, and after a week the garrison was obliged to sue for peace. The terms being agreed to, they came out the fort, and surrendered the keys to the officers of Chach, who gave them protection and showed them much kindness. He gave the chiefship of the place to Matta, and also placed one of his confidential officers there. He stopped there for a few days, during which time the affairs of the territory and the city were put in order.