佛說盂蘭盆經疏 2.20

2.20

Viewing and searching for the place of rebirth is the superknowledge of the divine eye. Because it was obtained through realizing the path, it is called the 'eye of the path'. As for 'the world', there are two kinds: the three realms are the world of vessels (bhājana-loka), and the six destinies are the world of sentient beings (sattva-loka). However, on the day the Venerable One lost his parents, he was still an ordinary person and did not know into which destiny his parents had been born. Now, having attained the noble fruit, his power was sufficient to seek them out; therefore, with the divine eye, he viewed upward and downward, searching for their bodies among the six destinies within the three realms. Because he viewed immediately upon obtaining the superknowledge, the text says 'immediately'.