佛說盂蘭盆經疏 1.7

1.7

Second, as for responding to the present request: it refers to Mahāmaudgalyāyana, who, out of the filial devotion of his original mind, wished to deliver his parents and repay the grace of nursing and nourishment. Therefore he left home and cultivated the practice, becoming foremost in supernatural powers, and observed that his deceased mother had fallen among the hungry ghosts. Unable to save her himself, he addressed the Buddha to seek the Dharma. The Buddha revealed the offering of the basin to rescue his mother from hanging upside down. Because he loved his parents, he extended this to all beings. For the sake of the monastic and lay disciples, he requested the Buddha to leave behind this dharma gate; responding to Maudgalyāyana's request is the reason for preaching the sūtra.