Rabi’ bin Amir (r.a.)
During the caliphate of Hz. Umar, the Muslims lived their golden age under the justice of Islam while the Islamic armies conquered new cities and countries, gained victories and expanded the Islamic land.
The Islamic army of 34 thousand soldiers under the command of Sa’d Ibn Abi Waqqas reached the Persian land. There was very little time left for the realization of the prayer of the Messenger of Allah (pbuh). As it is known, “Parwiz”, the Iranian ruler, tore the letter of the Messenger of Allah into pieces and the Messenger of Allah prayed against him as follows: “O Lord! Tear him and his land into pieces as he tore my letter into pieces!” This prayer came true and his son Shirwiya killed Parwiz with a dagger; now it was time for his land to be torn into pieces.
Rustam, the Iranian commander, did not want to fight the Islamic army due to some internal affairs and wanted to make peace. However, he made preparations for the war too. The Islamic army had 34 thousand soldiers but the Iranian army had 80 thousand soldiers along with 120 thousand reserves. 30 thousand soldiers had been chained to one another so that they would not escape. Despite this, Rustam was not very confident and demanded envoys frequently from Sa’d Ibn Abi Waqqas, the brave commander of the Islamic army, trying to stall for time.
The second envoy to go to Rustam was Rabi’ bin Amir. When he arrived, he saw a pompous scene he had never seen before. The place where Rustam stayed was embellished with embroidered pillows, velvet carpets, pearls and rubies and many other jewels. Rustam was sitting on a golden throne and the people around him served him like slaves.
Rabi had old clothes, a crooked sword, a somewhat bent shield and a shaggy horse. In fact, the pomp Rabi’ bin Amir saw did not appeal to him. In return for their pomp, he had an unshakable belief and indestructible courage.
When he arrived in the place covered with carpets, he dismounted from his horse and tied his horse. He had his weapon, armor and helmet on him. They said, “Leave your weapon.” He said, "I have not come here of my own accord. If you do not accept me like that, I shall return." The people there were astonished to hear such brave words from such a feeble person.
Rustam said, “Leave him!” Rabi’ proceeded and stuck his spear in the ground when he approached Rustam. There were silk pillows on the ground. The spear pricked the pillows. Those embellished pillows, which the people there gave great importance, were of no significance for Rabi’. The only thought in his mind was to fulfill his duty in a way that was suitable for the dignity of Islam.
Rustam said, “Start speaking.” Rabi’ started:
“Allah has sent us a prophet to save the people He wishes from worshipping people and to make them worship Him, to save people from the troubles of the world and to enable them to feel tranquil, to save them from the oppression of wrong religions and to enable them to attain the justice of Islam. If you accept Islam, you will become like us and we will return. If you do not accept Islam, we will fight you until we attain what Allah promised.
“What did Allah promise?”
“Paradise for those who die while fighting unbelievers and victory for those who survive.”
“I have listened to what you have said. Will you give us some time to think about this issue?”
“How many days?”
“One or two days.”
“No. This time is not enough for us to correspond with our scholars and leaders.”
“Our Prophet ordered us not to give respite to the enemy more than three days after facing them. Think, ask your men and choose one of the three options in that period: To accept Islam, to pay jizyah or to fight.”
"Are you their chief?"
"No. The Muslims are like one body, strengthening each other."
Thereupon, Rustam gathered his men and said, “Have you heard anything more valuable and acceptable than the words of this man?”
His men gave Rustam a harsh answer: “May God protect you from leaving your religion and tending to his religion. Have you not seen the clothes of that man? What can be the value of a man who wears such clothes?”
After a while, the Islamic army of 34 thousand soldiers consisting of people wearing clothes like Rabi’ beat the army of 200 thousand soldiers wearing embellished clothes and jewels. The Islamic army entered Madayin and witnessed the realization of the prayer of the Messenger of Allah (pbuh). Only 8 thousand people were martyred in the Islamic army and went to Paradise but 120 thousand people from the Iranian army were killed and the remaining ones escaped. 
Isaba, 1: 503; Hayatus-Sahaba, 1: 157.