Midrasch zu Wajikra 7:16

1) (Vayikra 19:5) "And if you slaughter a sacrifice of peace-offerings to the L–rd, for your will shall you slaughter it. (Vayikra 19:6) On the day that you slaughter it, it shall be eaten, and on the next day.": Let this not be stated, (for it has already been written, viz. [Vayikra 7:16]). If it is not needed for eating, learn it as applying to slaughtering, i.e., even when you slaughter it, your intent should be to eat it for two days.

6) (Vayikra 7:16) ("And if a vow or a gift is the sacrifice of his offering, on the day that he offers his sacrifice shall it be eaten, and on the next day, that which remains of it may be eaten.") This comes to teach about those offerings that are eaten for two days that they are eaten for two days. This tells me only of peace-offerings (viz. Vayikra 7:18). Whence do I derive (the same for) the festive offering (chagigah)? I would derive a festive offering that comes in its time (the first day of the festival). Whence would I derive a chagigah that comes (all seven days) as indemnity (for the first day), peace-offerings (of joy) that come in the midst of the festival (in addition to those of the chagigah and (left-over) peace-offerings (of joy) that come after the festival? From (the redundant) "And if a vow or a gift" (Vayikra 7:16).

7) Whence do we derive (the same for) the chagigah that comes with the Pesach (on the fourteenth of Nissan)? Because it is written (Devarim 16:4) "And there shall not remain of the flesh that you sacrifice towards evening on the first day until the morning," which teaches us about the chagigah of the fourteenth that it is eaten for two days and one night. I might think (that it is eaten) for one day and one night. It is, therefore, written "until the morning" — the morning of the second day. And how would I satisfy "a chagigah is eaten for two days"? (A different chagigah,) aside from this one. It is, therefore, written (to negate this, the redundant) "And if a vow or a gift."