俱舍論記 22.86

22.86

「若謂世尊至無非苦故」者，牒救徵破。若謂世尊於一苦受隨順世俗說三受者，不應正理。佛密說受無非苦故。若密意說，受皆是苦；若顯了說，受即有三種。既盡理說顯說有三，明知說三非隨世俗。

As for "If it is said that the World-Honoured One... because none are not suffering": this takes up the defence and interrogates to refute it. If it is said that the World-Honoured One, with respect to a single painful feeling, spoke of three feelings in accordance with worldly conventions, this is not reasonable, because the Buddha implicitly spoke of feelings as being nothing but suffering. If spoken with implicit intent, feelings are all suffering; if spoken explicitly, feelings are of three kinds. Since he spoke exhaustively of the principle and explicitly stated that there are three, it is clearly known that speaking of three is not in accordance with worldly conventions.