Bhagavad Gita 18.67
Do not speak this to one who has not practiced austerities, or to one who does not love, or who will not listen, or who mocks.
इदं ते नातपस्काय नाभक्ताय कदाचन।न चाशुश्रूषवे वाच्यं न च मां योऽभ्यसूयति॥idaṃ te nātapaskāya nābhaktāya kadācana|na cāśuśrūṣave vācyaṃ na ca māṃ yo'bhyasūyati||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).