Chapter 4 · Knowledge and Renunciation of Action · Krishna said
Bhagavad Gita 4.2 — Knowledge lost over time
एवं परम्पराप्राप्तमिमं राजर्षयो विदुः। स कालेनेह महता योगो नष्टः परन्तप ॥
evaṃ paramparāprāptamimaṃ rājarṣayo viduḥ | sa kāleneha mahatā yogo naṣṭaḥ parantapa ||
Meaning
Passed down this way from one to the next, the royal sages knew this yoga. But over a long time it was lost to the world, Arjuna.