Reference for Zevachim 191:4
דכיון דאיכא שתי הלחם ולחם הפנים דאפייתן בתנור וקדושתן בתנור הוה ליה כלי שרת וכלי שרת דחרס לא עבדינן
- Since the Two Loaves and the Shewbread<span class="x" onmousemove="('comment',' V. Lev. XXIII, 15-17; Ex. XXV, 30.');"><sup>7</sup></span> were baked in the oven and were sanctified in the oven, it became a service vessel, and we do not make earthen service vessels.<span class="x" onmousemove="('comment',' Offerings such as meal-offerings, loaves etc. were sanctified by being placed in service vessels. The Two Loaves and the Shewbread, however, were not placed in a service vessel, but were kneaded and shaped outside the Temple court, then brought in and baked in the oven. Thus the oven itself sanctified them, and ipso facto ranked as a service vessel.');"><sup>8</sup></span>