Комментарий к Бамидбар 26:11

ובני קרח לא מתו BUT THE SONS OF KORAH DID NOT DIE — They were in the plot originally, but at the moment when the rebellion broke out they had thoughts of repentance in their hearts; therefore a high spot was fenced round for them in Gehinnom and they stayed there (Sanhedrin 110a).

ובני קרח לא מתו. However, Korach's sons had not died. It is somewhat surprising that the Torah informs us about this fact here instead of in the story about Korach or in connection with the count of the Levites where we should have been told about which Levites had died. If you accept what we have written it is evident that the Torah chose this occasion to reveal who was the root-cause of Korach's uprising, i.e. Datan and Aviram. If so this was the place to inform us about some other redeeming quality of Korach, namely that his sons were righteous and did not join their father in his rebellion or that they retracted in time. At any rate, whereas Datan and Aviram and all their "houses," i.e. their offspring perished, Korach's sons did not. This is another factor which supports the theory that Datan and Aviram had been the instigators all along.

.ובני קרח לא מתו , “and Korach’s sons did not die.” Our sages in Megillah 14 explain these words to mean that there was a special place reserved for them in Gehinom where they remained. The site where the swallowing occurred and where judgment of these individuals occurs is known as Gehinom. Alternatively, the sages meant the real purgatory the entrance to which is close to the point where Korach and company were swallowed. (According to Eyruvin 19 there are a total of three such portals to purgatory). We find that sons (or descendants) of Korach sang hymns in the Holy Temple as we know from Psalms 47,1 and 48,1 and others.