Bhagavad Gita 18.68
But he who teaches this great secret to My devotees, his is the highest devotion, and he shall surely come to Me.
य इमं परमं गुह्यं मद्भक्तेष्वभिधास्यति।भक्ितं मयि परां कृत्वा मामेवैष्यत्यसंशयः॥ya imaṃ paramaṃ guhyaṃ madbhakteṣvabhidhāsyati|bhakitaṃ mayi parāṃ kṛtvā māmevaiṣyatyasaṃśayaḥ||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).