Pesachim 37A

ובית הלל מתירין. וכמה פת עבה? אמר רב הונא: טפח, שכן מצינו בלחם הפנים טפח.

And Beit Hillel permit one to bake bread in this manner. The Talmud asks: And how much thickness is required for the matza to be considered thick bread? Rav Huna said: This category includes matza that is a handbreadth thick. The proof is as we found by the showbread, which could not be leavened and which was a handbreadth thick.

מתקיף לה רב יוסף: אם אמרו בזריזין ⁠— יאמרו בשאינן זריזין? אם אמרו בפת עמילה ⁠— יאמרו בפת שאינה עמילה?

Rav Yosef strongly objects to this explanation: If the rabbis said that it is permitted to bake bread a handbreadth thick for the showbread, which was prepared by diligent priests who ensured that the dough did not become leavened, will they say the same with regard to other people who are not as diligent? Furthermore, if they said this with regard to well-kneaded bread, will they say the same with regard to bread that is not well kneaded?

אם אמרו בעצים יבשין ⁠— יאמרו בעצים לחים? אם אמרו בתנור חם ⁠— יאמרו בתנור צונן? אם אמרו בתנור של מתכת ⁠— יאמרו בתנור של חרס?

Rav Yosef continues: If they said that bread a handbreadth thick is permitted in a case where the bread was cooked with dry wood, which was brought to the Temple during the dry summer months, as the heat generated from this type of wood would cause the bread to cook quickly before it leavened, will they say the same with regard to ordinary people who cook with moist wood? If they said this with regard to a hot oven in the Temple, will they also say it is permitted with regard to a cool oven? Finally, if they said so with regard to the showbread, which was baked in a metal oven that could be heated quickly, will they say the same with regard to a clay oven? Clearly, these two cases are different, and no comparison can be drawn between the showbread and ordinary matza.