What is the ruling on the annual interest from a savings account at the post office, and is it permissible to pay it as a fee for a barber to style and adorn the fiancée for the wedding ceremony?

Savings accounts in usurious institutions are loans with interest, which is usury (riba) by scholarly consensus. It is not permissible to own an account book in a usurious institution. Whoever has done so must repent, withdraw their savings, and spend theurious interest on the welfare of Muslims with the intention of disposing of the unlawful money. It is not permissible to spend it on anything that would benefit the person or ward off harm from them. Therefore, it is not permissible to pay for the adornment of the fiancée from those interest earnings.