Abu Ubaida the Commander-in-Chief of the Muslim forces in Syria died of plague in 639 A.D. Other Muslim Generals who fell victims to plague included Shuhrabil b. Hasana and Yazeed bin Abi Sufyan. On the death of the senior Generals, Amr bin Al-Aas was appointed as the Commander-in-Chief of the Muslim forces in Syria.

Amr bin Al-Aas belonged to the Bani Sahm clan of the Quraish. Like the other Quraish chiefs, Amr opposed Islam in the early days. He commanded a Quraish contingent at the battle of Uhud. In 630 A.D. in the company of Khalid bin Waleed, Amr bin Al-Aas rode from Mecca to Madina and there both of them were converted to Islam. Thereafter Amr took part in all the campaigns fought by the Muslims.

There is a story that in the days of ignorance when Amr was young he travelled once to Palestine with a caravan. One day it was the duty of Amr to shepherd the camels of the caravan in the plain outside Jerusalem. It was a hot day, and as Amr sat under the shade of a tree, he saw a weary traveller come that way. The traveller appeared to be in a bad state because of thirst. Amr placed his water skin at the disposal of the traveller who drank to his fill. Having quenched his thirst the traveller lay to rest under a nearby tree and soon he was sleep.

A little later Amr saw a snake crawl out from a hole and proceed to the sleeping traveller. Amr took out his bow and shot an arrow at the snake which fell dead. After some time the traveller woke to find that a dead snake lay near him. He asked Amr as to what had happened, and Amr told him that he had shot at the snake.

Turning to Amr, the traveller said, "You have saved my life twice firstly when I was dying of thirst, and secondly when I was exposed to the danger of the snake". He said that he would pay him an amount equivalent to the blood money for two lives. He stated that he had come to Jerusalem on a pilgrimage from Egypt. He was a priest in Egypt. He wanted Amr to accompany him to Egypt where he would pay the blood monely. Amr hesitated to visit Egypt but the Egyptian priest painted such a rosy picture of Egypt that the curiosity of Amr was excited and he ultimately agreed to accompany the Egyptian priest.

Amr and the Egyptian priest travelled to Egypt. Throughout the journey the priest looked after all the needs of Amr. When they reached Alexandria Amr was lodged in a magnificent mansion and treated as a royal guest. The host of Amr took him to attend the festival at the Hippodrome. One of the rites performed at the festival was the Golden Ball rite. A high priest struck a golden ball and sent it flying in the air. The belief was that he in whose sleeve the golden ball landed would be the ruler of Egypt. When the high priest struck the garden ball every one followed the path of the golden ball with tense expectation. As the ball curved in the air, it landed in the sleeve of Amr. The spectators were dumbstruck. They could not believe that an uncouth Arab from the desert could rule over Egypt. They thought that there had been some mistake somewhere in the shooting of the golden ball.

The host of Amr said to him, "Congratulations for one day you will rule over Egypt. How you will come to rule over Egypt I cannot say, but this omen from the gods on high can never be false. Strange are the ways of destiny and who knows some day you may come here as the ruler of Egypt."

Amr returned from Egypt loaded with gifts and money. The episode of the golden ball always remained fresh in the memory of Amr. He often tried to dismiss it as an idle dream, but in his heart of hearts there was a strong conviction that some day he would march to Egypt as its victor.

When Amr became the Commander-in-Chief of the Muslim forces in Syria, he incessantly thought of Egypt and his destiny to conquer it. Umar visited Syria in 639. On this occasion Amr waited on Umar and said:

"O Commander of the Faithful, permit me to march on Egypt. It will be a source of strength and sustenance for the Muslims. It is the richest of lands on earth".

Umar was not favourably inclined to the proposal, but Amr persisted. Ultimately Umar gave way and he said:

"Go and I shall seek Allah's guidance in the matter of your going. If on your march you receive a letter from me and I wish you to turn back then turn back if you have not entered Egypt by that time. If you have crossed the frontier when you receive my letter, then you may proceed and may God help you."

Having wrung this conditional permission from Umar Amr bin Al-Aas took a contingent of 4,000 picked soldiers and immediately took the road to Egypt.