Allah Ta‘ala had blessed Hazrat Sa’d (radhiyallahu ‘anhu) by allowing the conquer of ‘Iraq to take place at his hands. It was the armies under his command that defeated the Romans in Qaadisiyyah. However, Hazrat Sa’d (radhiyallahu ‘anhu) could not personally lead the army in this specific battle, as he was ill and sores had broken out across his entire body, and so he informed the people of his illness and excused himself from joining them in fighting against the kuffaar.
After the battle was over, a person, despite knowing the predicament of Hazrat Sa’d (radhiyallahu ‘anhu), began to criticize him and tried to spur people against him through reciting the following poetry:
ألم تر أن الله أنزل نصره وسعد بباب القادسية معصم
Do you not see that Allah Ta‘ala has sent down His assistance, while Hazrat Sa’d (radhiyallahu ‘anhu) is safely guarded (through not fighting) at the door of Qaadisiyyah?
فأبنا وقد آمت نساء كثيرة ونسوة سعد ليس فيهن أيم
We are returning while many of our wives have become widows, and there is no widow among the wives of Hazrat Sa’d (radhiyallahu ‘anhu).
When Hazrat Sa’d (radhiyallahu ‘anhu) heard the poetry in which this person was falsely accusing him of being cowardly and refraining from fighting without any excuse, he made du‘aa saying, “O Allah! Cut his tongue and hand on my behalf!”
Soon thereafter, an arrow struck his mouth, rendering him dumb, after which his hand was cut off while fighting. This person was later on killed by the disbelievers.
(Siyar A’laam min Nubalaa 3/72, Majma‘uz Zawaa’id #14856)