Fukan zazengi

[1] It is traditionally thought to have been composed in 1227, shortly after Dōgen's return to Japan from his years of study in China.

However, a manuscript of Fukan zazengi discovered in modern times that was produced by Dōgen's own hand ends with a Colophon (publishing) stating it was written in 1233.

There is also a Shōbōgenzō book entitled Zazen gi, composed sometime between 1243 and 1246, that appears to draw material from the vulgate Fukan zazengi and thus suggesting it would not have been written afterwards.

Regardless of the exact date of its first composition, it is clear the material went through many rounds of editing over the author's lifetime.

[2] Much of the section describing the actual practice of zazen is copied from the Zuochan yi, a meditation manual written by Changlu Zongze in the early 12th century.