瑜伽論記 1.264

1.264

夢有七緣，四由闇相作意思惟者，景師云：於法不了名為闇相，而樂思惟法於前發夢，更有一解，瞑目思惟黑闇色相故，致於睡夢。

Dreaming has seven conditions. Regarding the fourth, "through attentiveness reflecting on dark characteristics": Master Jing says: Not comprehending dharmas is called "dark characteristics," and taking pleasure in reflecting on dharmas beforehand generates dreams. There is another explanation: Closing the eyes and reflecting on the characteristic of dark form induces sleep and dreams.