俱舍論記 1.108

1.108

「亦名三有至三有攝故」者，此有漏法亦名三有。三有即是欲有、色有及無色有。與三有為因，因即集諦；與三有為依，依即苦諦；復是三有攝故。具斯三義，故名三有。

Regarding "They are also called the three realms of existence [...] because they are subsumed under the three realms of existence": these sāsrava dharmas are also called the three realms of existence (tri-bhava). The three realms of existence are the realm of desire, the realm of form, and the formless realm. They serve as the cause for the three realms of existence—the cause being the truth of origin; they serve as the support for the three realms of existence—the support being the truth of suffering; and furthermore they are subsumed under the three realms of existence. Possessing these three meanings, they are therefore called the three realms of existence.