Manava Dharmashastra 5.20

5.20

amatyā abuddhipūrvaṃ ṣaṭ jagdhvā ṣaṇṇāmanyatamamapi | bhakṣyasya avidheyatvanimittatayā sāhityasyāvivakṣā | śeṣeṣu abhakṣyeṣu bhakṣaṇe lohitavṛkṣaniryāsādiṣu ekamahorātraṃ na bhuñjīta | ahaḥśabdo rātrāvapi dṛṣṭaprayogaḥ | "ahaśca kṛṣṇamahararjunaṃ ceti” (ṛgveda 6 |

Medhātithi’s commentary (manubhāṣya):
This refers to the Brāhmaṇa who is in the habit of eating at the house of those Śūdra whose food he is permitted to eat.