Bhagavad Gita · 18.68

य इदं परमं गुह्यं मद्भक्तेष्वभिधास्यति।भक्तिं मयि परां कृत्वा मामेवैष्यत्यसंशयः॥

ya idaṁ paramaṁ guhyaṁ mad-bhakteṣhv abhidhāsyati bhaktiṁ mayi parāṁ kṛitvā mām evaiṣhyaty asaṁśhayaḥ

One who teaches this supreme secret to My devotees, showing highest devotion to Me, shall undoubtedly come to Me.

— Bhagavad Gita 18.68

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)