After an invite from Ben:
The text is
《坐禪三昧經》 No. 614
(CBETA, T15, no. 614, p. 269, c25-28)
It is not in the standard Agama collections. This does not mean that it is not equivalent to an Agama text, though, as sometimes individual texts were translated as one-offs, and sometimes these were even put elsewhere. In particular, because it was translated by Kumarajiva, and the later arrangers of the Chinese canon tend to assume that Kumarajiva is Mahayanist (and he is), they may just put anything by him in that category. Often, though, Kumarajiva produced a lot of Sarvastivadin and similar works. It is in the Taisho along with other "dhyana sutras", but not in the volumes with the full Agamas or one-off agama sutras.
This text would probably make some Theravadins think that it is Mahayanist, simply on the grounds of "if it has things that are not in our suttas or texts, then it must be Mahayanist." For example, practices of visualizing the Buddha. But it is not that simple, and it simply reflects ideas that were prevalent in a lot of other mainstream schools at that time. It apparently has a verse on dhyana in it from Asvaghosa. Yinshun believes it to be a text from the Darstantikas (Yinshun 1985: 205-06, 1091: 862), and he is probably correct. I am a bit surprised that Ven Analayo did not check out Ven Yinshun, because as far as things like this go, he is the expert par excellence! The Darstantikas are the meditative / sauntrantika side of the Sarvastivada, so this is perhaps why the order and other features are more similar to the Theravada Nikayas than the Sarvastivadin Agama layout.
Anything else that you are specifically looking for?
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