Midrash for Chagigah 34:5

ואי אשמעינן בהא בהא קאמרי ב"ה משום דלא אפשר למחר אבל בהא אימא מודו לב"ש צריכא

And if [the Mishnah] only taught us this [first statement regarding the possibility of a make-up slaughtering day, we would think that] in this case, the House of Hillel say [that there is no slaughtering day], because it is impossible to bring them the next day; but here [in a normal case], they would agree with the House of Shammai [that one may not bring the offerings on Yom Tov].

Sifrei Devarim