Begging is not permissible but for one of the three (classes) of persons

Messenger of Allah (Sallallähu alaihi wa sallam) said, "Begging is not permissible but for one of the three (classes) of persons:

1. One who has incurred debt, for him begging is permissible till he pays that off, after which he must stop it.
2. A man whose property has been destroyed by a calamity which has smitten him, for him begging is permissible till he gets what will support life, or will provide him reasonable subsistence.
3. A person who has been smitten by poverty.

...besides these three (every other reason) for begging is forbidden, and one who engages in such consumes that what is forbidden."

Book: Sahih Muslim 2271