What is the (middle length) sutta, where Buddha exposes a monk, who has an ignorant view of non-self? In one sutta a monk was teaching, that there's something that is behind our existence, that is permanent (opposite of non-self). Buddha asked for this explicitely, got confirmed, and corrected the view. Which sutta it is?
Possibly MN 38, where the monk held:

At one time the Lord was staying near Sāvatthī in the Jeta Grove in
Anāthapiṇḍika's monastery. Now at that time a pernicious view like
this had accrued to the monk called Sāti, a fisherman's son: “In so
far as I understand Dhamma taught by the Lord it is that this [same;
identical; <a
href="https://suttacentral.net/define/ana%C3%B1%C3%B1a" rel="nofollow noreferrer">anañña]
consciousness itself runs on, fares on, not another.&quot;

Note: I chose the translation of I.B. Horner to avoid the contradictory eternalism of the other translators, who use words such as &quot;transmigration&quot; or add words that do not even exist in the sutta, such as &quot;round of rebirths&quot;.