Mimamsasutra 105.2

105.2

iti cet paśyasi - yadi deśasaṃyogād ākhyā bhavet, deśāntarasthasya na bhavet. bhavati ca deśānatarasthasya māthura ity asaṃbaddhasyāpi mathurayā. tasmān na deśasaṃyogād ākhyā.

If you think this: "If the name were due to connection with a place, it would not apply to one residing in another country; yet the name 'one from Mathurā' (Māthura) does apply to one residing in another country, even when unconnected with Mathurā. Therefore, the name is not due to connection with a place."—