Bhagavad Gita Chapter 13
Powerful Cognition
A person who knows how to handle his body and mind enjoys the whole thing.
He is totally at ease with himself.
kṣetrajñaṁ cāpi māṁ viddhi sarvakṣetreṣu bhārata kṣetra-kṣetrajñayor jñānaṁ yat taj jñānaṁ mataṁ mama
O Bhārata, know that I am the Knower in all bodies [kṣetrajña], the witness. In my opinion knowledge means the understanding of this body or the field of activity as well as the Knower of this field