Reference for Pesachim 120:7

אלמא אתי שלא לשמו ומפיק ליה מידי לשמו כי שחיט נמי לשמו ושלא לשמו אתי שלא לשמו ומפיק ליה מידי לשמו

will you say [the same where it is slaughtered] for its own purpose, seeing that it does not operate [as a cause of disqualification] in the case of all [other] sacrifices but only in the case of the Passo sacrifice alone? What is [our decision] thereon? - Said Raba, A Passover sacrifice which he slaughtered at any other time of the year for its own purpose and for another purpose is fit.

Jastrow