法苑珠林 72.20

72.20

又善見律云。佛言。龍有五事不得離龍身何者為五。一行婬時。若與龍共行婬得復龍身。若與人共行婬不得復龍身。二受生不離龍身。三脫皮時。四眠時。五死時。是為五事不得離龍身。

Furthermore, the Shanxian lü says: The Buddha said: Dragons have five circumstances in which they cannot shed the dragon body. What are the five? First, at the time of copulation: if they copulate with a dragon, they can revert to a dragon body; if they copulate with a human, they cannot shed the dragon body. Second, when taking birth, they do not shed the dragon body. Third, at the time of shedding their skin. Fourth, when asleep. Fifth, at the time of death. These are the five circumstances in which they cannot shed the dragon body.