俱舍論頌疏論本 25.39

25.39

釋曰：六種羅漢得滅定者，名俱解脫，先由慧力解脫惑障，又得滅定解脫定障，故名為俱。

Explanation: Those among the six kinds of arhats who attain the absorption of cessation are called 'liberated both ways': first, through the power of wisdom they are liberated from the hindrance of affliction; further, they attain the absorption of cessation and are liberated from the hindrance to concentration; therefore they are called 'both'.