金剛般若經疏論纂要 1.56

1.56

即無住處涅槃，不共二乘，故云第一。無著云：「何故願此？不可得義生所攝故。」又云：「卵、濕、無想、有頂則不能。」云何普入？有三因緣：一、難處生者待時故，二、非難處生，未成熟者成熟之故，三、已成熟者解脫之故。

This is non-abiding nirvāṇa, which is not shared with the two vehicles; therefore it is called 'supreme'. Asaṅga says: "Why make this vow? Because it is subsumed under the meaning of unattainable [beings to be delivered]." He also says: "Those born from eggs, moisture, the perceptionless, and the peak of existence are unable [to enter immediately]." How then are they universally led to enter? There are three causes and conditions: first, for those born in places of difficulty, one waits for the proper time; second, for those not born in places of difficulty who are not yet mature, one matures them; third, for those already matured, one liberates them.