Manava Dharmashastra 2.158

2.158

ṣaṇḍho napuṃsaka ubhayavyañjano'śaktaḥ strīgamane, yathā strīṣvaphalaḥ | yathā gaurgavi strīgauḥ strīgavyām | evaṃ tathā vipro'nṛco'nadhīyāno'phalaḥ | saptāṣṭaślokāḥ adhyetṛveditroḥ praśaṃsārthā atikrāntāḥ |

As the eunuch is useless among women, as the cow is useless among cows, as a gift to the ignorant person is useless, even so is the Bbrāhmaṇa useless who is devoid of the Veda.—(158)

Medhātithi’s commentary (manubhāṣya):
‘Eunuch’—he who is without masculine virility, having both (male and female) signs and incapable of intercourse with women,—just as this person is ‘useless women’;—as again is ‘the cow useless among cows’;—‘even so is the Brāhmaṇa useless who is devoid of the Veda,’—i.e., who does not learn.—(158)

This verse is quoted in Vīramitrodaya (Saṃskāra, p. 511) as deprecating ignorance of the Veda;—and in Smṛticandrikā (Saṃskāra, p. 129) to the effect that all acts are futile for one who is ignorant of the Veda.

Comparative notes by various authors
Parāśara-smṛti (Prā. 8-18).—(Reproduces Manu with a slight verbal variation.)

Vyāsa (Vīramitrodaya-Saṃskāra, p. 511).—‘For one who is devoid of the Veda, all actions are futile.’

Vaśiṣṭha (Do,).—‘One bereft of the Veda is not a Brāhmaṇa.’

Hārīta (Do., p. 512).—‘The Veda is what should be learnt by the Brāhmaṇa.’

Mahāhhārata, 12.36.47.—(First half the same as Manu)—‘as the bird is without wings, so is the Brāhmaṇa devoid of Mantras.’