Bhagavad Gita, Chapter 4, Verse 29

Yet some offer as sacrifice the outgoing breath into the incoming, and the incoming into the outgoing, stopping the courses of the incoming and outgoing breaths, constantly practising the regulation of the vital energy; while others, with regulated food, offer the functions of the Prânas as sacrifice.

Even something as basic as breathing can become a genuine practice, once it's done with real intention behind it.

This describes people who turn the most automatic, unnoticed function of the body into a deliberate discipline. Breath control here isn't a technique for its own sake, it's another form of that same underlying offering.