Manava Dharmashastra 2.201

2.201

parīvādāt kharo bhavati śvā vai bhavati nindakaḥ
paribhoktā kṛmir bhavati kīṭo bhavati matsarī //

By censuring (his teacher), though justly, he will become (in his next birth) an ass, by falsely defaming him, a dog; he who lives on his teacher's substance, will become a worm, and he who is envious (of his merit), a (larger) insect.