I have found SN 22.88 about Assaji, who is supposed to be one of the first five Arahants, which was sick then and failed to attain concentration whom finally the Buddha came to help with this discourse.
Some consider this Assaji is diferrent from the first Arahant Assaji, but I found this unsatisfactory for me because the commentary are silent about this sutta. I think this sutta is one of sources of the notion that an Arahant still can fall away, a very notion that has been debated since early Buddhism period.
What do you think, are this notion supported by this sutta (and its parallel in SA)?
To my mind the EBTs are quite clear that an arahant cannot fall away. The arahant has “ended birth” (khīṇā jāti), has made an end of suffering (dukkhassa antakāro), has achieved “unshakable freedom of mind” (akuppa cetovimutti), etc., etc. All of these suggest a final attainment from which it is not possible to fall away. From what I know all of these are also found in the Āgamas.
Given this strong evidence, I do not think SN 22.88 can be used to support the post-EBT idea of arahants falling away. There are too many other plausible explanations for what we see in this sutta. It is quite possible that this is a different Assaji. It may have been a fairly common name at the time. Or it is possible that the Assaji of the group of five did not actually become an arahant during the delivery of the Anattalakkhaṇa-sutta (SN 22.59). Please keep in mind that the information about the arahantship of the five monks is only found in the narrative section of this sutta, and as such it may not be reliable information. It could even be that the information about arahantship in SN 22.59 means that all five monks eventually became arahants. This would have been much easier for the rectors of the canon to assess than whether they became arahants while the sutta was actually spoken.
In sum, I doubt that this sutta can be used as support for such a controversial idea.