pf2e.fyi
From Pathfinder Howl of the Wild, which isn't enabled.

Tenacious Endurance

FEAT 6
ARCHETYPEEMOTIONMENTAL
Archetype Beastmaster
Prerequisites Beastmaster Dedication

You encourage your companion to refuse to yield, against even the mightiest of foes. When one of your animal companions is reduced to 0 Hit Points, if it isn't wounded, it can remain standing with 1 Hit Point and become Wounded 1.

Pathfinder Howl of the WildORC