Now Gersiwaz, when he beheld the anger of the King, deemed that the time was ripe. He therefore gave a sign unto the men that held Saiawosh in bondage, and desired that they should slay him. And by the hairs of his head they dragged him unto a desert place, and the sword of Gersiwaz was planted in the breast of the royal cedar. But when it was done, and they had severed the head from the trunk, a mighty storm arose over the earth, and the heavens were darkened. Then they trembled and were sore afraid, and repented them of their deed. And clamour arose in the house of Saiawosh, and the cries of Ferangis reached even unto Afrasiyab her father.
This passage demonstrates that magnitude of Saiawosh in comparison to the surrounding universe, so to speak. The third sentence highlights this, as Saiawosh's death caused turmoil in weather, along with "the heavens", regardless of what religious ideology that one possesses, they are still experiencing the fallout from the killing of Saiawosh.