He gave his zakaah to a poor man who turned out to be well off
Question

                I gave zakaah on my wealth to a poor man, then after that I found out that he was well off. Does this zakaah count as such?.
Praise be to Allah.
    The scholars differed concerning one who gives his zakaah to 
    one who is well off, thinking that he is poor. The Shaafa’is are of the view 
    that it does not count as such. See al-Majmoo’ (6/225). 

    The Hanbalis are of the view that it does count, and this is 
    the correct view. 

    This is indicated by the report narrated by al-Bukhaari 
    (1421) and Muslim (1022) from Abu Hurayrah (may Allaah be pleased with him), 
    that the Messenger of Allaah  (peace and blessings of Allaah be upon 
    him) said: “A man said, ‘I am going to give charity’  … He went out with his 
    charity and placed it in the hand of a rich man. The next morning, they 
    said, ‘Last night he gave charity to a rich man.’ He said: ‘O Allaah, to You 
    be praise for a rich man. … It was said to him: ‘As for your charity, it has 
    been accepted. … As for the rich man, perhaps he will learn a lesson and 
    spend from that which Allaah has given him.” 

    A person’s poverty may not be apparent, so it is sufficient 
    for the one who is giving zakaah to think that he most likely poor. Allaah 
    says (interpretation of the meaning): 

    “The one who knows them not, thinks that they are rich 
    because of their modesty. You may know them by their mark, they do not beg 
    of people at all”

    [al-Baqarah 2:273]. 

    Al-Bahooti said in Kashshaaf al-Qinaa’ (2/296): If he gives 
    him zakaah thinking that he is poor then he turns out to be well off, that 
    is still valid. End quote. 

    Does the same ruling apply in all cases where he gives zakaah 
    to people thinking that they are entitled to it, then he finds out that they 
    were not entitled to it, such as one who gives his zakaah to a kaafir, 
    thinking that he is a Muslim, or he gives it to a poor man, the finds out 
    that he is one of the descendents of the Prophet  (peace and blessings 
    of Allaah be upon him)? 

    The Hanbalis are of the view that it dos not count as zakaah 
    in these cases, because in most cases such things are not hidden from 
    people, unlike poverty, which may be hidden. See al-Mughni (2/281). 

    Shaykh Ibn ‘Uthaymeen favoured the view that it does count as 
    zakaah in these cases. He said in al-Sharh al-Mumti’ (6/265): If he 
    gives it to someone who he thinks is entitled to it after checking on him, 
    then he finds out that he was not entitled to it, that still counts as 
    zakaah, because he feared Allaah as much as he could, and Allaah says 
    (interpretation of the meaning): 

    “Allaah burdens not a person beyond his scope”

    [al-Baqarah 2:286].  

    What counts in acts of worship is what the person thinks, 
    unlike interactions with others, where what counts is the reality of the 
    transaction, not what the person thinks.  

    End quote.