Manava Dharmashastra 5.35

5.35

niyuktas tu yathānyāyaṃ yo māṃsaṃ nātti mānavaḥ
sa pretya paśutāṃ yāti saṃbhavān ekaviṃśatim //

But a man who, being duly engaged (to officiate or to dine at a sacred rite), refuses to eat meat, becomes after death an animal during twenty-one existences.