Reference for Pesachim 120:5

ואמר לי לא אם אמרת בשלא לשמו שכן נוהג בכל הזבחים תאמר בלשמו שכן אינו נוהג בכל הזבחים אלא בפסח בלבד

it from [the disqualifying effect of] another purpose,<span class="x" onmousemove="('comment',' So that if it is killed both for its purpose and for another purpose, it is unfit.');">⁹</span> so also [the slaughtering] for another purpose, which makes it fit at a different time, does not save it [from the disqualifying effect] of its own purpose, and it is unfit.

Jastrow