金剛般若經疏 1.22

1.22

經。還至本處　演曰。第三歸本趣得支身不令過分。又由知足故乞不過量知時故還至本處。及如來食有種。一受請。二不受請。今不受請故須還歸。又表還源返本歸真住寂將說般若深妙理故。又釋國城雙舉因緣。即是此中往還所以。

Sūtra: ...he returned to his original place.
Commentary: The third is returning to the source: seeking only enough to sustain the body and not letting it be excessive. Furthermore, due to knowing contentment, he did not beg beyond measure; knowing the time, he returned to his original place. Moreover, there are two kinds of eating for the Tathāgata: 1. accepting invitations; 2. not accepting invitations. Here, not accepting invitations, he must return. Furthermore, it symbolizes returning to the source and reverting to the root, returning to truth and abiding in quiescence, being about to preach the profound and subtle truth of prajñā. Another explanation is that the dual mention of country and city above serves as the reason for coming and going here.