Bhagavad Gita · 4.3

स एवायं मया तेऽद्य योगः प्रोक्तः पुरातनः।भक्तोऽसि मे सखा चेति रहस्यं ह्येतदुत्तमम्॥

sa evāyaṁ mayā te 'dya yogaḥ proktaḥ purātanaḥ bhakto 'si me sakhā cheti rahasyaṁ hy etad uttamam

That very same ancient yoga has been today taught by Me to you, because you are My devotee and friend. This is indeed a supreme secret.

— Bhagavad Gita 4.3

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