Bhagavad Gita 4.2

एवं परम्पराप्राप्तमिमं राजर्षयो विदु: |
स कालेनेह महता योगो नष्ट: परन्तप

Translation

O subduer of enemies, the saintly kings thus received this science of Yog in a continuous tradition. But with the long passage of time, it was lost to the world.