Is it proven that ‘Umar (may Allah be pleased with him) wrote a letter to the Nile in Egypt so that its water would flow by Allah’s leave?
Question

                I want to know the authenticity of the story about Umar (may Allah be pleased with him) writing a letter to the River Nile. It seems to me as illogical, for the Qur'aan and the Saheeh saheeh Sunnah (authentic prophetic traditions) do not teach such a thing. Also, that for droughts, Salah Salat Ul al Istisqa is authentically established.
Praise be to Allah.
    Ibn 
    Katheer (may Allah have mercy on him) said: 

    It was 
    narrated to us via Ibn Luhay‘ah from Qays ibn al-Hajjaj from someone who 
    told him: When Egypt was conquered, its people came to ‘Amr ibn al-‘As (may 
    Allah be pleased with him) and said to him: O Ameer, this Nile of ours is 
    used to something and cannot flow unless it is done. He said: What is that? 
    They said: On the twelfth night of this month, we take a young girl from her 
    parents, and we placate her parents, then we dress her in jewellery and the 
    finest garments there can be, then we throw her into this Nile. 

    ‘Amr (may 
    Allah be pleased with him) said to them: This is something that cannot 
    happen in Islam; Islam erases that which came before it (of bad customs). 

    So they 
    stayed for a while, during which the Nile did not flow at all, neither a 
    little nor a lot, until they thought of leaving. Then ‘Amr (may Allah be 
    pleased with him) wrote to ‘Umar ibn al-Khattab (may Allah be pleased with 
    him), telling him about this. He wrote to him, saying: You did the right 
    thing. I am sending you a piece of paper with my letter; throw it into the 
    Nile. 

    When his 
    letter came, ‘Amr (may Allah be pleased with him) took the piece of paper on 
    which was written: 

    “From the 
    slave of Allah ‘Umar, Ameer al-Mumineen, to the Nile of the people of Egypt.

    To 
    proceed: If you only flow on your own initiative, then do not flow, for we 
    have no need of you. But if you only flow on the command of Allah, the One, 
    the Subduer, and He is the One Who causes you to flow, then we ask Allah, 
    may He be exalted, to make you flow.” 

    He threw 
    the paper in the Nile and by Saturday morning, Allah had caused the Nile to 
    flow (to a depth or width of) sixteen cubits in one night, and Allah put an 
    end to this particular custom of the people of Egypt until today.

    End quote 
    from al-Bidayah wa’n-Nihayah, 7/114-115 

    Similar 
    reports were also narrated by Ibn ‘Abd al-Hakam in Futooh Misr, p. 165; 
    al-Lalkai in Sharh I‘tiqad Ahl as-Sunnah, 6/463; Ibn ‘Asakir in Tareekh 
    Dimashq, 44/336; Abu’sh-Shaykh in al-‘Azamah, 4/1424, via Ibn Luhay‘ah. 

    This is a 
    da‘eef isnad (weak chain of narration) that is not saheeh, and this report 
    cannot be proven with such an isnad. Ibn Luhay‘ah – whose full name was 
    ‘Abdullah ibn Luhay‘ah ibn ‘Uqbah – is da ‘eef as he used to get mixed up, 
    and in addition to that he is mudallis (one 
    who 
    narrates from someone he met something he did not hear). 
    See at-Tahdheeb, 5/327-33; Mizan al-I‘tidaal, 2/475-484 

    Qays ibn 
    al-Hajjaj is sadooq (trustworthy), from the sixth level of hadeeth narrators 
    (tabaqah) according to al-Hafiz Ibn Hajar; they are the ones who it is not 
    proven that they met any of the Sahabah/Companions (may Allah be pleased 
    with them). See: Taqreeb at-Tahdheeb, 1/25 

    Sometimes 
    he narrated it as a mursal (the 
    link between the Successor and the Prophet is missing) 
    report and 
    sometimes he narrated it from the one who told him, but the one who told him 
    is majhool and not known. 

    So the 
    report is da‘eef (weak) and is not saheeh (sound) 

    If this 
    story were true, everyone would know about it and it would be well known, 
    and it would have been widely narrated through confirmed isnads, because it 
    is an important and significant event, the like of which should not be 
    ignored; rather an incident less significant than this would not be 
    overlooked by historians and narrators. 

    And Allah 
    knows best.