Secret of the Golden Flower

From:
https://ia802902.us.archive.org/22/items/SecretOfTheGoldenFlower_201809/...

and

https://archive.org/details/SecretOfTheGoldenFlower_201809

"This ancient esoteric treatise was transmitted orally for
centuries before being recorded on a series of wooden
tablets in the eighth century. It was recorded by a member of
the Religion of Light, whose leader was the Taoist adept Lu
Yen (also known as Lu Yen and Lu “Guest of the Cavern”). It
is said that Lu Tzu became one of the Eight Immortals using
these methods. The ideas have been traced back to Persia
and the Zarathustra tradition and its roots in the Egyptian
Hermetic tradition."