I taught this imperishable yoga to Vivasvan. Vivasvan declared it to Manu, and Manu told it to Ikshvaku.
Explanation
Krishna opens this chapter by tracing the origin of the teaching he has been giving Arjuna. Vivasvan is the sun-god, Manu is the progenitor of humankind, and Ikshvaku is the ancestor of the solar line of kings. Yoga (the disciplined path of union with the divine, here linked to acting with wisdom and without attachment) is called imperishable (avyaya) because its truth does not decay. Commentators differ on whether this yoga means mainly karma-yoga, knowledge-centred yoga, or the whole teaching of the Gita.