Incident of when the Persion King spoke to the Sahabah...

On the first day of the battle of Al-Qaadisiyyah, the Persians traveled from al-Heerah until they reached al-Qaadisiyyah at the bridge called al-‘Ateeq, facing the Muslim camp, with the river in between. The Persian king, Rustam, sent a word to Sa’d Ibn Abi Waqqaas (the leader of the Muslim army) saying: “Send us a man with whom we may speak.” 

So he sent Rab’ee Ibn ‘Aamir, who came to him and found him sitting on a throne of gold, with carpets and cushions interwoven with gold thread. Rab’ee Ibn ‘Aamir came riding his horse, with his sword in a sheath of cloth and his spear tied around with a cloth. When he reached the carpets he made his horse step over them, then he dismounted and tied his horse with two pillows that he tore apart. Then he took the saddlecloth and wrapped it around himself (like a cloak). 

They gestured that he should put down his weapon, so he said: “If I had come to you on my own initiative, I would do what you ask, but you are the ones who called me.” 

Then he came, leaning on his spear and taking small steps so as to do more damage to the carpets on which he was walking. When he came near to Rustam (the Persian king), he sat on the ground and stuck his spear into the carpet and said: “We do not sit on your furniture.” 

Rustam asked him: “What brought you here?”

He said: “Allah brought us here. He has sent to us to bring whomsoever He wills from the worship of other people to the worship of Allah, from the constriction of this world to its ease, and from the injustice of other religions to the justice of Islam. He sent to us His Messenger, bringing His religion to His creation. Whoever accepts it, we will accept that and leave him and his land alone, but whoever refuses, we will fight him until we end up either in Paradise or in victory.” 

Rustam said: “We have heard what you said. Can you give us some time to think about it?” 

He said: “Yes, one of the things that the Messenger of Allah (saws) taught us is not to give the enemies more than three days. So we will leave you alone for three days. Think about it, and choose one of three options: 
(1) either become Muslims, and we will leave you and your land alone; 
(2) or pay the jizyah and we will accept it and leave you alone, and if you need us we will come to your help; or 
(3) fight on the fourth day, unless you start it before then. I guarantee that to you on behalf of my companions.” 

Rustam asked: “Are you their leader?” 

He said: “No, but the Muslims are like a single body, part of one another, and the highest of them accepts a commitment made by the lowest of them.” 

Then he went away and Rustam consulted with his companions and said: “Have you ever heard anything like what this man has said?” 

They tried to make little of him, but Rustram said: “Woe to you, I am thinking of his wisdom, eloquence and behaviour. The Arabs do not care about clothes, but they pay a great deal of attention to lineage.” 

On the second and third day Rustam again asked to see someone with whom he may speak. On the third day after the third person had left, Rustam consulted with the Persians and said: “Who are they in comparison to you? The first two came and boldly figured you out, then this one came with the same approach. They have all followed the same method and acted in the same way. By Allah, these are real men whether they are sincere or are liars. By Allah, if their discipline and their way of keeping secrets has reached such a level that they all have the same approach, never differing, there are no people who are able to achieve what they want like them. If they are sincere, no one will be able to stand up to them.” 

[‘Umar Ibn Al-Khattab, His Life And Times, Pp.168-170]