Reference for Eruvin 3:6

אמר רב יהודה אמר רב חכמים לא למדוה אלא מפתחו של היכל ורבי יהודה לא למדה אלא מפתחו של אולם

only from the [dimensions of] the entrance to the Hekal<span class="x" onmousemove="('comment',' or 'Holy', was situated between the Ulam, the hall leading to the interior of the Temple, and the Debir or the Holy of Holies, and contained the golden altar, the table for the shewbread and the candlestick.');">¹⁸</span> and R'Judah could only have deduced it<span class="x" onmousemove="('comment',' The ruling as to the proper measurements of an entrance. kfhv');">¹⁷</span> from the [dimensions of] the entrance to the Ulam.<span class="x" onmousemove="('comment',' V. previous note.');">¹⁹</span> For we have learnt: The entrance to the Hekal<span class="x" onmousemove="('comment',' V. previous note.');">¹⁹</span>

Rashi on Sukkah