Adhyāya 166: Kṛtaghna-doṣa (कृतघ्नदोषः) — the fault of ingratitude and the limits of expiation
उदपानोदके ग्रामे ब्राह्मणो वृषलीपति: । उषित्वा द्वादश समा: शूद्रकर्मेव गच्छति
udapānodake grāme brāhmaṇo vṛṣalīpatiḥ | uṣitvā dvādaśa samāḥ śūdrakarmāiva gacchati ||
ভীষ্মে ক’লে—যি গাঁৱত সকলোৱে একে কুঁৱাৰ পানী পান কৰে, তাত শূদ্ৰা-স্ত্ৰীৰ স্বামী হৈ বাৰ বছৰ বাস কৰিলে ব্রাহ্মণো শূদ্ৰৰ কৰ্ম-আচৰণত গ’ল বুলি গণ্য হয়।
भीष्म उवाच
The verse teaches that varṇa-identity and eligibility for particular dharmas are not treated as merely nominal; sustained association, marriage alliance, and long-term residence within a community—together with adopting its customary occupations—can lead society to regard a person as having shifted into that community’s mode of life and duties.
In the Śānti Parva’s dharma-instruction, Bhishma is laying down a rule-like observation about social status: a Brahmin who marries a Śūdra woman and lives for twelve years in a village characterized by common use of a single well is said to ‘go to’ (i.e., be classed as) one following Śūdra conduct/occupation.