自有潔淨 Somewhere Clean to Talk
三藏答禮道：「此間不是講話處，待貧僧到那寺觀，卻好行事。」郡侯道：「老師同到小衙，自有潔淨之處。」三藏答礼道：「此间不是讲话处，待贫僧到那寺观，却好行事。」郡侯道：「老师同到小衙，自有洁净之处。」
逐句解 Line by line
Tripitaka returned the courtesy. "This is no place to talk," he said. "Let this poor monk get to a temple or a monastery, and then the business can be done properly."
寺觀 pairs the Buddhist temple with the Daoist monastery — a compound meaning religious premises of either kind, which is a nicely practical way to ask for a venue. 那 here is nà, the ordinary that — the word simply points at something. The reading only shifts to nǎ when it is asking a question.
The prefect said, "Come with me to my own government office, master. There is a clean place to be had there."
小衙 is my little yamen — a yamen being the local government office, the walled site where an official worked, judged cases and had his home, all on one plot. Calling it little is politeness, not description. 潔淨, clean and pure, means ritually fit rather than merely swept.
Tripitaka's first instinct is to get the prefect off the ground and out of the street, and he does it by raising a practical objection about the venue. It is tactful and slightly bureaucratic, which is very much his register.
The exchange also quietly relocates the chapter. Everything from here to the rainfall happens indoors, in a government compound — the pilgrims are about to conduct a cosmic negotiation from the reception hall of a provincial office. Few episodes in the novel are staged so domestically.