俱舍論記 25.17

25.17

「退法種姓至通三界皆有」者，別釋立名。六種姓中，前之五種但約容有建立此名，故六阿羅漢通三界皆有。

Regarding "The lineage of falling-away dharma ... exist across all three realms": this individually explains the establishment of the names. Among the six lineages, the preceding five are established in name merely based on possibility; therefore, the six arhats exist across all three realms.