Praise be to Allah.
The basic principle concerning zakaah is that it should be given to the poor of the country where the wealth on which it is paid is, and it should not be transferred elsewhere unless there is a need or an interest to be served. The Prophet (blessings and peace of Allah be upon him) said to Mu‘aadh when he sent him to Yemen: “…teach them that Allaah has enjoined on them charity (zakaah) to be taken from their rich and given to their poor …” Narrated by al-Bukhaari, 1395; Muslim, 19.
If he transfers it when there is no need or interest to be served, then he has done wrong, but it is still acceptable and he is not to be instructed to pay it again.
It says in Kashshaaf al-Qinaa‘ (2/263): It is not permissible to transfer it from the place where it is as far as the distance at which it becomes permissible to shorten prayers, even if it is being transferred to a relative or because of severe need or to be given to other categories of people who are entitled to zakaah. However, if he goes against that ruling and does that, it is acceptable because of the general meaning of the texts and because he has given it to one who is entitled to it, so it is paid off, like a debt. End quote.
It says in al-Mawsoo‘ah al-Fiqhiyyah (23/332): Moreover, if you transfer zakaah without a good reason for doing so, as mentioned above, the Hanafis and Shaafa‘is, and the Hanbalis, are of the view that it is acceptable, because it was not given to anyone other than the eight categories (of those who are entitled to zakaah). The Maalikis say that if he transfers it to a place where there are poor people whose need is equal to that of those who are in the place where he is living, it is acceptable even though it is haraam, and if he transfers it to people who are in less need than them, it is not acceptable, according to what was stated by Khaleel and al-Dardeer. ad-Dasooqi said: The correct view is that it is valid in any case. End quote.
The authors of al-Mawsoo‘ah quote the Shafaa‘is as saying that if zakaah is transferred to another land, it is acceptable. There are two opinions concerning this matter that have been narrated from Imam al-Shaafa‘i (may Allah have mercy on him; the more correct view according to his companions is that it is not acceptable. See: al-Majmoo‘, 6/212; Asna al-Mataalib, 1/403; Futoohaat al-Wahhaab, 4/109.
Shaykh Muhammad ibn Ibraaheem (may Allah have mercy on him) was asked about the ruling on transferring zakaah to another land that is as far away as the distance at which shortening prayers becomes permissible or further.
He replied: There are two scholarly opinions concerning this matter. The well-known view according to later scholars is that it is not allowed, unless there are no poor people in the land where the wealth is. The other opinion is that it is permissible if there is an interest to be served by transferring it. This view was favoured by Shaykh Taqiy ad-Deen. Shaykh ‘Abdullah ibn Muhammad ibn ‘Abd al-Wahhaab said, and this is the view we adopt, that it is acceptable. And it is valid according to both views
End quote from Fataawa al-Shaykh Muhammad ibn Ibraaheem, 4/98
He also said: Those who are of this opinion differed as to whether zakaah is acceptable in this case or not. The well-known opinion is that it is acceptable even though it is haraam or makrooh to transfer it.
End quote from Fataawa al-Shaykh Muhammad ibn Ibraaheem, 4/99
To sum up: Zakaah should be given in the land where the wealth is, unless there is a legitimate purpose to be served by transferring it elsewhere, in which case there is nothing wrong with doing that. Legitimate interests in this regard include transferring it to one’s relatives, because that will bring a greater reward, or transferring it to people who are in greater need. This has been discussed in the answer to question no. 43146.
And Allah knows best.