Adhyāya 166: Kṛtaghna-doṣa (कृतघ्नदोषः) — the fault of ingratitude and the limits of expiation
गोब्राह्मणहितार्थ च वर्णानां संकरेषु च | वैश्यो गृह्नीत शस्त्राणि परित्राणार्थमात्मन:,गौ और ब्राह्मणोंका हित, वर्णसंकरताका निवारण तथा अपनी रक्षा करनेके लिये वैश्य भी हथियार उठा सकता है
bhīṣma uvāca | gobrāhmaṇahitārthaṃ ca varṇānāṃ saṅkareṣu ca | vaiśyo gṛhṇīta śastrāṇi paritrāṇārtham ātmanaḥ ||
Bhishma said: For the welfare of cows and Brahmins, for preventing the confusion and intermixture of social orders, and for his own protection, even a Vaishya may take up weapons.
भीष्म उवाच
Bhishma teaches that taking up arms can be dharmic even for a Vaishya when it serves higher protective aims—safeguarding cows and Brahmins, preventing varna-confusion, and ensuring self-preservation. The permissibility is grounded in protective duty rather than aggression.
In the Shanti Parva’s instruction on dharma and social order, Bhishma lays out exceptions and responsibilities across varnas. Here he states that, under threats to societal stability and to protected groups, a Vaishya is permitted to bear weapons for defense and protection.