It has been related that after the conquest of Egypt, the people there came to newly appointed governor Amr Bin al-A’as and said:
” It is one of our ancient customs to make some offering to the River Nile in this month of the year. And if we don’t do that, then the water level does not rise. Our offering to the River Nile is made on the 12th of this month. We select a virgin – she has to be the only child of her parents whom we pay heavily to hand her over to us. Then we take the child, dress her up, and adorn her with all sorts of jewellery. Then we cast her into the river. Thereafter, the water level rises, otherwise it doesn’t. “
The valiant conquerer of Egypt Amr Bin al-A’as replied, “This is a foolish custom reeking of ignorance. Islam does not permit anything like that. Islam has wiped out all such customs. ”
So the people refrained from it.
The water level of the Nile did not rise. The entire month passed but the river-bed remained dry. As people could not bear it any longer because they depended on the water of the river, they decided to leave Egypt.
Amr Bin al-A’as thought it appropriate to inform the Caliph- Sayyidina Umar Bin al-Khattab (RA) – about the situation. Sayyidina Umar sent the following reply;
” You did the right thing. I am sending you a letter addressed to the River Nile. Take it and throw it into the river.”
Amr Bin al-A’as took the letter which read as follows;
” From Allah’s slave, the commander of the faithful, Umar,
to the Nile, the river of the people of Egypt.
After praising Allah and invoking blessings on Allah’s messenger, ( I proceed to say that) If you flow on your own and according to your own will and pleasures, then don’t flow. And if Allah, the One, the Omnipotent makes you flow, then we pray to Allah to make you flow again. “
Amr al-A’as took this letter and threw it into the Nile as instructed.
One night had barely past, and the water level of the Nile had risen to 16 cubits. Aridity and famine gave way to fertility and affluence. Hardship gave way to comfort and ease. Through the blessings of this letter, Egypt became verdant and green. The River Nile has been flowing since. And there was no need for any further human sacrifices. Thus Egypt was purged once and for all from this impure custom.
(Tafsir Ibn Kathir 4/213)