四分律行事鈔資持記 3.859

3.859

六中，《四分》，初安便器。次第三開。屋中，即房內。不下，次置唾器。既制污地，必有所盛故。

In the sixth [section]: The Dharmaguptaka first places chamber pots, sequentially opening three [locations]. "Inside the house" means within the room. "Not" below next places spittoons. Since defiling the ground is prohibited, there must be something to contain it.