妙法蓮華經玄義 4.68

4.68

三禪，用雷音三昧者，此禪樂最深，如氷魚蟄蟲，是果報著樂，又著空樂、假樂、中樂。為驚駭諸樂，修諸雷音之行。餘如上說。

For the third dhyāna, the thunder-sound samādhi is used: the bliss of this dhyāna is the deepest, like ice-bound fish or hibernating insects; this is clinging to the bliss of retribution, and furthermore clinging to the bliss of emptiness, the bliss of the provisional, and the bliss of the Middle. In order to startle these blisses, he cultivates the practices of thunder sound. The rest is as explained above.