Skandapurana 6.3.50.4

6.3.50.4

yathā ṣaṇḍho'phalaḥ strīṣu yathā gaurgavi cāphalā .
yathā cājñe'phalaṃ dānaṃ tathā vipro'nṛco'phalaḥ .. 50.4 ..

Just as a eunuch is fruitless among women, just as a cow with a cow is fruitless, / and just as a gift given to an ignorant man is fruitless, so a brahmin devoid of the Ṛgveda is fruitless.