Disallowance under section 40(b): interest to a partner disallowed even if representing an HUF; direct HUF receipt permitted. Payment of interest by a firm to a partner is subject to disallowance under Section 40(b); the prohibition is absolute and covers interest paid to a partner even when he claims to represent a Hindu Undivided Family. By contrast, interest paid directly to an HUF (and not to a partner) is not disallowable.