Aśauca-vidhi (Rules of Impurity) within Śrāddha-kalpa — Chapter on Testing/Selecting Brahmanas and Honoring the Atithi
एतैस्तु वर्त्तयेद्यस्तु कृष्णवर्णं स गच्छति / यो ऽश्नाति सह शूद्रेणा सर्वे ते पङ्क्तिदूषणाः
etaistu varttayedyastu kṛṣṇavarṇaṃ sa gacchati / yo 'śnāti saha śūdreṇā sarve te paṅktidūṣaṇāḥ
He who lives by these practices goes to the state called kṛṣṇa-varṇa. Whoever eats together with a Śūdra—all such are declared defilers of the sacred dining line.