Is it permissible for a Hashemite who is unable to work to take charity from people, even if he does not know whether it is zakat or not?

It is not permissible for Banu Hashim to take obligatory zakat, due to the saying of the Prophet, peace and blessings be upon him: "Do you not know that the family of Muhammad, peace and blessings be upon him, do not eat charity?" As for voluntary charity, there is no harm for them in taking it.

Sheikh al-Islam Ibn Taymiyyah chose the permissibility for them to take from the obligatory zakat to alleviate their necessity if they are deprived of their share of the spoils (one-fifth of the fifth), which Sheikh Ibn Uthaymeen supported, explaining that this is the correct opinion because they are in need and necessity in the absence of the one-fifth in our current time.