Bhagavad Gita Chapter 18, Verse 67

इदं ते नातपस्काय नाभक्ताय कदाचन | न चाशुश्रूषवे वाच्यं न च मां योऽभ्यसूयति ||

idam te nātapaskāya nābhaktāya kadācana na cāśuśrūṣave vācyaṁ na ca māṁ yo 'bhyasūyati

This should never be spoken by you to one who is without austerity, who is not a devotee, who does not want to hear, and who reviles Me.

Krishna gives a warning about sharing this teaching. 'Idam te nātapaskāya nābhaktāya kadācana'—this (idam) should never (na kadācana) be spoken by you (te) to one who is without austerity (atapaskāya), who is not a devotee (abhaktāya). 'Na cāśuśrūṣave vācyaṁ na ca māṁ yo 'bhyasūyati'—and (ca) not (na) to one who does not want to hear (aśuśrūṣave) should it be spoken (vācyam), and (ca) not (na) to one who reviles (abhyasūyati) Me (mām). This is the instruction: this most secret teaching should not be shared with those who are not ready—those without austerity, those who are not devotees, those who don't want to hear, and those who revile Krishna. This teaching is precious and should only be shared with those who are ready and receptive. Sharing it with those who are not ready will not help them and may cause harm.