"Great Void Elixir Scripture" is the most prestigious and universally accepted classic in the Cultivation World.
The "Great Void Elixir Scripture" stated in its opening dialogue what the superior method of refining pills is: "Use the great void as the cauldron, the Taiji as the furnace, purity as the foundation of the pill, inaction as the Dantian, life and character as the mercury, and the five internal organs as the fire."
This is where the Samadhi True Fire comes from, and as such, it is often revered as the treasure for refining pills by Pill Masters.
The Samadhi True Fire can refine heavenly and earthly treasures and likewise, in a certain sense, cultivators are also considered heavenly and earthly treasures, so you can imagine the consequence if it encounters cultivators.
Lu Yang's Three Flavored True Fire is derived from the Samadhi True Fire, though it is somewhat less potent, but it is not to be trifled with.