Ghalib ibn Dha al-Nun. He entrusted him with receiving the booty and distributing the fayʾ, appointed Salman al-Farisi as the army’s caller and preacher, and assigned Ziyad ibn Abi Sufyan as his scribe.
They say:
In that entire force there were three hundred-odd Companions, a little over seventy of whom had fought at Badr, together with seven hundred sons of the Companions (may Allah be pleased with them).
ʿUmar dispatched a letter to Saʿd ordering him to hasten to al-Qadisiyyah—regarded in the pre-Islamic era as Persia’s gateway—to position himself between the desert and the settled lands, to take control of the roads and passes into Persia, and to strike the enemy first with firmness and force. Let not the multitude of their men and their equipment alarm you ⦗1⦘; they are a people of trickery and deceit. If you remain patient, seek reward ⦗2⦘, and intend to fulfil the trust ⦗3⦘, I hope you will be granted victory over them. Thereafter they will never reunite with true resolve, for their hearts will not be with them. Should matters turn otherwise, fall back until you reach al-Hijr, for there you ⦗4⦘ will be the bolder, they the more cowardly, and their knowledge of the terrain the poorest, until Allah grants the conquest and restores the advantage to you.
He instructed him to call himself to account and to admonish his army, commanding them to keep a sound intention and to be steadfast, for victory descends from Allah in proportion to one’s intention, and reward in proportion to one’s hopeful expectation. Seek Allah’s protection and say often: “There is no might nor power except with Allah, the Most High, the Most Great.” Keep me informed in detail of all your circumstances—where you camp and where the enemy stands—so that through your letters I might see you with my very eyes. Make the matter clear to me; fear Allah, place your hope in Him, and claim no personal merit ⦗5⦘. Know that Allah has taken charge of this affair in a way that will never be revoked, so beware lest He turn it away from you and replace you with another people.
Saʿd wrote back, describing the encampments and the land so vividly that it was as though ʿUmar were seeing them himself. He informed him that the Persians had set Rustam and those like him in motion for war; they are pursuing us even as we pursue them. The command of Allah is proceeding, and His decree is accepted ⦗6⦘ for what He has allotted to us and against us. We ask Allah for the best decree and the best destiny, together with well-being.
ʿUmar replied:
“Your letter has reached me and I have understood it. When you meet your enemy and Allah turns them in flight before you, it has been cast into my heart that you will rout them—so do not doubt it. Once you have overcome them, do not cease your pursuit until you have stormed their capital, for that will be its destruction, if Allah wills.”
ʿUmar devoted himself to supplicating—especially for Saʿd, and, more generally, for all the Muslims.