瑜伽論記 4.224

4.224

於甘露界繫念思惟如是方入無漏定者，或四諦觀或觀二空，所顯真如為前方便入無漏定名甘露界。

Regarding "focusing mindfulness and reflecting upon the deathless realm, only in this way entering taintless concentration": whether through contemplation of the four truths or contemplation of the two emptinesses, the tathatā revealed thereby serves as the preliminary means for entering taintless concentration, which is named the "deathless realm."