Answer
(Fatwa: 828/828=M/1430)
It is unlawful and haram to have interest-based dealings. We are unaware of the system and procedure of National Saving. If you know that it is based on interest and most of your father’s income is earned through interest, you should avoid using his money as much as possible. Keep on convincing your father politely to look for a lawful job and leave this one when he finds a suitable lawful job.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband