Mahabharata — Anushasana Parva, Shloka 8
Cyavana’s Water-Vow and the Ethics of Cohabitation (स्नेह-सम्वास-धर्मः)
वैषम्यादथवा लोभात् कामाद् वापि परंतप । ब्राह्मणस्य भवेच्छूद्रा न तु दृष्टान्तत: स्मृता
vaiṣamyād athavā lobhāt kāmād vāpi paraṃtapa | brāhmaṇasya bhavec chūdrā na tu dṛṣṭāntataḥ smṛtā ||
毗湿摩说道：“噬敌者啊，无论出于偏私、贪欲，还是情欲，首陀罗（Śūdra）女子也可能成为婆罗门（Brāhmaṇa）之妻；然而在诸《沙斯特拉》（śāstra）中，并不记载此事为被认可的先例或法则。”
भीष्म उवाच
Educational Q&A
Bhishma distinguishes between what may happen in practice due to bias, greed, or desire and what is actually authorized by śāstra: an occurrence does not automatically become dharma unless supported by recognized scriptural precedent.
In his instruction to the king, Bhishma discusses norms of conduct and social regulation, noting that certain cross-varṇa marital outcomes can occur through human failings, but he denies that such cases are upheld as a formal rule in the remembered tradition.