Which is the discourse in which the distinction between khandhas in and of themselves and khandhas clung to, with the former being associated with the Buddha or arahants and identified as non-harmful, is made explicit?
Talk of the “purified skandhas” of arahants and Buddhas is a common feature of Indian scholastic Buddhism, both Abhidharmist and Mahayanist. But as far as I know, arahants are never spoken of in this way in the Suttas.
My mistake. The discourse never says it, but the fact that I read it in to the discourse says a lot about the way upādānakkhandha is read/ understood/translated. That this view is quite pervasive is supported by the fact that the discussion @Mike_0123 linked and B Bodhi’s comments were even necessary.