Siege of Fustat
After the conquest of Syria, Hazrat Amr bin Aas (ra) led the conquest of Egypt. When Hazrat Amr bin Aas (ra), the conqueror of Egypt, decided to attack Alexandria, he set up camp to the south of Alexandria along the edge of the River Nile. For this reason, that area is known as Fustat. Later it was developed into a city and the more recently developed part of that city is today known as Cairo.
When the Muslim besieged the Fustat, Hazrat Amr bin Aas (ra), observing the strong fortification of the fortress and his lack of soldiers in his army, sent a request to Hazrat Umar (ra) to send reinforcements. Subsequently, Hazrat Umar (ra) sent an army of 10,000 soldiers and four generals. Hazrat Umar (ra) also stated that each general was equivalent to 1,000 soldiers and Hazrat Zubair (ra) was one of those four generals.
When Hazrat Zubair (ra) arrived, Hazrat Amr bin Aas (ra) assigned him to oversee the arrangements of the siege. Hazrat Zubair (ra) mounted on a horse and took an inspection of the fortress and then arranged the armies. He assigned the cavalry and the infantry their respective positions and then ordered the catapults to pelt the fortress with rocks. The siege lasted for seven months but with neither any conclusive victory, nor loss as the outcome.
One day, Hazrat Zubair (ra) stated that he would sacrifice himself for the Muslims and with this drew his sword and climbed the ladder and stood on top of the outer wall of the fortress. A few other companions climbed with him and all of them raised the slogan of takbir [Allah is the greatest], the rest of the army also raised the slogan in such a forceful voice that the floor of the fortress began to reverberate. The Christians thought that perhaps the Muslims had entered into the fortress and thus fled in a state of utter perplexity. Hazrat Zubair (ra) then came down from the outer wall and opened the door of the fortress and the entire Muslim army marched through.
(Roshan Sitarey, Ghulam Baari Saif Sahib, Vol. 2, pp. 54-55), (Mu‘jamul Buldan, p. 259, al-Faisal Urudu Bazaar, Lahore, 2013)