The Book of Zakat (Kitab Al-Zakat)
Muslim :: Book 5 : Hadith 2271
Qabisa b. Mukhariq al-Hilali said: I was under debt and I came to the Messenger of Allah (may peace be upon him) and begged from him regarding it. He said: Wait till we receive Sadaqa, so that we order that to be given to you. He again said: Qabisa, begging is not permissible but for one of the three (classes) of persons: one who has incurred debt, for him begging is permissible till he pays that off, after which he must stop it; 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; and a person who has been smitten by poverty. the genuineness of which is confirmed by three intelligent members of this peoples for him begging is permissible till he gets what will support him, or will provide him subsistence. Qabisa, besides these three (every other reason) for begging is forbidden, and one who engages in such consumes that what is forbidden.