Is the money of a relative who does not pay zakat on his wealth, because he is illiterate and does not know the gravity of the matter of zakat, lawful for his family?

This person should be advised and reminded of the importance of Zakat and the punishment for neglecting it. He must pay Zakat for past years because it is not forfeited by ignorance or by the passage of time. Scholars differed on whether Zakat is tied to the person's liability (dhimma) or to the specific asset (ayn al-mal). According to the first view, his spending is permissible, though he sins by not paying; according to the second view, his wealth is mixed with what he owns and what he does not own. The preponderant view is that it is permissible to eat from mixed wealth, though it is disliked.