Reference for Shabbat 266:12
מתקיף לה רב פפא אומן לימא להו אנא עבדי פלגא דמצוה אתון עבדיתו פלגא דמצוה אלא אמר רב פפא גדול
because it is said, [And thou shalt set upon the table shewbread] before me alway.<span class="x" onmousemove="('comment',' Ex. XXV, 30. ');"><sup>22</sup></span> R. Jose said: Even if these remove and the other replace [it later], that too constitutes 'alway'.<span class="x" onmousemove="('comment',' I.e., 'alway' merely indicates that a night must not pass without shewbread lying upon the table. But the Rabbis hold that an interval would mark a new placing, not a continuation of the old, and so 'alway' would be unfulfilled. Similarly, when one withdraws from circumcision, to return for the shreds is a new act, hence not permitted unless these invalidate circumcision. ');"><sup>23</sup></span>