It was an ancient custonn with the Egyptians that some time in July a virgin decked in bridal clothes was thrown in the river as an offering to propitiate the God of the river Nile. Even when the Egyptians became Christians they continued to follow the ancient custom of sacrificing a virgin.
When Egypt came under Muslim rule, the Egyptian elders waited on Amr in July, and wanted his permission for continuing the old custom of throwing a virgin in the river to seek the pleasure of the God of the Nile.
Amr said that such a practice was repugnant to Islam and could not be permitted in an Islamic State. He argued that Islam knew of no God of the Nile and the question of any propitiation did not arise. Islam knew of only one God Allah and Allah did not stand in need of any propitiation.
The Egyptian elders listened to the argument but they did not feel satisfied. They warned Amr that unless the sacrifice was offered as heretofore the Nile would not rise in flood and the entire countryside would get arid.
Amr was however adamant that floods or no floods human sacrifice could not be permitted. The Egyptian leaders retired in a sullen mood.
The month of July passed away. No sacrifice was offered, and there was no rise in the level of the river. It was the month of August and still the river did not rise. The Egyptians shuddered at what would happen if the river did not rise. The month of August passed away and still there was no flood in the river. The Egyptian leaders sighed and said, "That is all due to Islam. The Muslims have brought this fate on us."
And even during September there was no sign of any rise in the level of the river. The Egyptians gave themselves to despair and most of them thought of migrating elsewhere.
That made Amr anxious. He reported the facts of the case to Umar and wanted his instructions. Umar approved of the action of Amr in not permitting the human sacrifice. Along with the letter, Umar sent a card on which it was written:
"In the name of Allah the Beneficent, the Merciful. From the slave of Allah, Umar Commander of the Faithful to the Nile of Egypt.
Everything in the Universe is subject to the will of Allah. The rise in your level is subject to the will of Allah, and we pray to Allah to command you to rise in level."
Umar asked Amr that the card should be thrown in the middle of the river. On the eve of the Feast of the Christian Day of the Cross, Amr had the Christians assemble on the river bank and after reciting some verses from the Holy Quran and taking the name of God he threw the card of Umar in the middle of the river. Then the Muslims assembled on the river bank lifted their hands in prayers seeking the blessings of God in making the river rise in level. The card of Umar floated on the surface of the Nile for some distance and then it disappeared.
The next morning the river rose to its full flood height. Verily Allah had commanded the river to flow, and that was the end of the evil custom of sacrificing a virgin to secure a rise in the level of the river. That was the vindication of Islam. Many Egyptians now came to believe that Islam was a blessing and a true religion. They hastened to the Muslim camp and were converted to Islam.