四分律刪繁補闕行事鈔 2.214

2.214

If persons are individually invited, one should perform the procedure to announce the call outside the gate; if even a single person is obtained, it is deemed pure; if the procedure is not performed and there is no one within the boundary, all the monks still incur the offense of food obstruction impurity. If judged by these words, it does not yet depend on failure to assemble within the boundary; even if all assemble, an offense is still incurred. Hence the text states: 'If four people are individually invited and sit in order side by side among the saṃgha to receive and eat food, not sharing the same flavors with the saṃgha, an offense is incurred with every swallow.'