Reference for Shabbat 263:9

גדול דכתיב ביה ברית לידחי שבת

and we do not argue a minori from a traditional law! — Rather said R. Eleazar: We learn 'a sign' [written in connection with circumcision from] 'a sign' [written in connection with the Sabbath].<span class="x" onmousemove="('comment',' Circumcision: and it shall be a sign of a covenant betwixt me and you (Gen. XVII, 11); Sabbath: for it is a sign between me and you (Ex. XXXI, 13). Since both are so designated, it follows that the former must be performed even on the latter. ');">⁸</span>

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