Reference for Chagigah 51:9

ובירושלים נאמנין על הקודש: תנא נאמנין על כלי חרס גסין לקודש וכל כך למה שאין עושין כבשונות בירושלים:

(Mishnah:) And in Jerusalem they are trusted regarding holy things: (Gemara:) It was taught [in a Baraita]: "They are trusted regarding [even] large clay vessels with regard to holy things. And all this, why? Because they would not make furnaces in Jerusalem [with which to make vessels, forcing them to trust the <i>Amei Ha'Aretz</i>.

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