The Yoga Sūtras

One hundred and ninety-six aphorisms so compressed they are unusable without a commentary — which is how they were always meant to be read. Eight limbs, beginning with restraint and observance and ending in samādhi.

The classical frame that modern practice claims and rarely follows. Worth pairing with David Gordon White's history: much of what is now taught as ancient yoga is a twentieth-century construction, and the sūtras themselves went comparatively neglected for centuries before being revived as a flagship text.