Bhagavad Gita 1.40
कुलक्षये प्रणश्यन्ति कुलधर्माः सनातनाः। धर्मे नष्टे कुलं कृत्स्नमधर्मोऽभिभवत्युत।।1.40।।
kulakṣaye praṇaśyanti kuladharmāḥ sanātanāḥ| dharme naṣṭe kulaṃ kṛtsnamadharmo'bhibhavatyuta||1.40||
kulakshaye pranashyanti kuladharmah sanatanah dharme nashte kulam kritsnamadharmo'bhibhavatyuta1.40
Meaning
Arjuna argues that when a family is destroyed, its ancient traditions of dharma perish. When dharma is lost, the entire family is overcome by adharma (unrighteousness).
कुल के नाश से सनातन कुलधर्म नष्ट हो जाते हैं। धर्म के नष्ट होने पर समस्त कुल को अधर्म दबा लेता है।
This is verse 40 of 47 in Chapter 1 (Arjuna Vishada Yoga) of the Bhagavad Gita.