What is the ruling on not giving to beggars whose need is doubted?

There is no objection to not giving voluntary charity to beggars whose need is doubtful. However, if you do give it, you will receive its reward, even if they are not in need, because voluntary charity can also be given to the wealthy. As for obligatory charity, such as zakat (definition), it should not be given to them if their eligibility is doubtful. Rather, one must be certain or have a strong presumption that they are among its rightful recipients. If a person pays zakat while doubting whether the recipient falls under its categories, and they have not investigated, or they have investigated and it has not become clear to them that the person is a rightful recipient, then that payment is invalid.