Reference for Zevachim 211:4

אמר ליה אביי דילמא במקומו משופך פליגי

For it was taught: Where the ashes are poured out it shall be burnt: [this intimates] that ashes must be there [first]. R'Eliezer B'Jacob said: It intimates that the ground must slope down.<span class="x" onmousemove="('comment',' Lit., 'poured out', it must be a place where the ashes naturally pour down.');"><sup>3</sup></span>