Reference for Pesachim 177:12
מאי נפקא מינה והא תנן כל הניתנין על מזבח החיצון שנתנן במתן אחת כפר
and declare, 'If mine was blemished, let this which I bring now be a passover-offering; while if mine was unblemished, let this which I bring now be a peace-offering,' for a Passover 'remainder' is eaten one day and one night [only]?<span class="x" onmousemove="('comment',' If an animal is consecrated as a Passover-offering but not sacrificed as such, it is a Passover-'remainder', which is then brought as a peace-offering but eaten only during the shorter period. Hence here, let each consecrate the animal for a Passover-offering. If his animal was blemished, he discharges his duty with this one. But if his animal was unblemished, this is automatically a Passover-'remainder', since it cannot be sacrificed for its own purpose (Tosaf.; Rashi explains slightly differently.)');"><sup>9</sup></span>