法華義疏 6.35

6.35

此既明內德，則有息化之義，如臥之像。故《涅槃》云「入大涅槃深禪定窟，眾不見故名入涅槃」。今於縟上更安枕，譬於禪定內入般涅槃也。又佛有時間乃至八萬劫入深三昧，亦是息化，故是欲臥之像。

Since this clarifies internal virtues, it contains the meaning of resting from teaching activities, resembling the image of reclining. Therefore the Mahāparinirvāṇa Sūtra says: 'Entering the cavern of deep meditative concentration of great nirvāṇa, unseen by the multitude, is called entering nirvāṇa.' Now placing a pillow further upon the bedding symbolizes entering parinirvāṇa within meditative concentration. Furthermore, the Buddha at times enters deep samādhi for as long as eighty thousand kalpas, which is also resting from teaching activities; hence it is the image of reclining.