佛說盂蘭盆經疏 2.98

2.98

四輩者，僧尼士女，或云人天龍鬼，疑故兩存。然凡厥生靈皆依恃怙，故父母恩均於天地。此雖至孝不得其門，今受神方信知靈驗，必能除七世之厄難、報二親之劬勞。自知心有所之，是以歡喜承命。

"Four assemblies": monks, nuns, laymen, and laywomen; or it is said to mean humans, devas, dragons, and ghosts. Because there is doubt, both are preserved. However, all living beings rely upon their father and mother; therefore, the kindness of parents equals heaven and earth. Although these [beings] had supreme filial piety, they had not found its gateway; now having received the divine prescription, they faithfully know its efficacious proof, that it can certainly eliminate the tribulations of seven lifetimes and repay the toils of the two parents. Knowing in themselves that their minds had attained their goal, they therefore rejoiced and accepted the command.