分別功德論 4.29

4.29

所以稱施羅一坐一食者，此謂頭陀一行也。夫阿練法，或乞食、或坐樹下、或閑居獨處。今此一坐一食者，從早起至日中，若檀越施食，不問多少，其於一處坐食而已。若食未飽坐未移者可得更食，若已起者不得復食。常一處食而不捨離，故稱施羅為第一。

The reason why Śīla is said to eat at one sitting is that this refers to a practice of the dhūtas. In the practice of an āraṇyaka, one may beg for food, sit under a tree, or dwell alone in solitude. Now, eating at one sitting means that from early morning until noon, if a dānapati provides food, no matter how much or little, he simply sits in one place and eats. If he is not yet full and has not moved from his seat, he may eat more; but if he has already risen, he must not eat again. Constantly eating in one place without departing, Śīla is therefore called foremost.