Bhagavad Gita Chapter 4.2
evaḿ paramparā-prāptam
imaḿ rājarṣayo viduḥ
sa kāleneha mahatā
yogo naṣṭaḥ parantapa
Translation
This supreme science was thus received through the chain of disciplic succession, and the saintly kings understood it in that way. But in course of time the succession was broken, and therefore the science as it is appears to be lost.