“and nothing of the flesh which you offered in the evening should remain on the night of the first day over until the morning.” (Devarim 16,4)
It is a negative commandment not to leave over any of the flesh from the Chagiga of the fourteenth until the third day. The chagigah is the sacrifice which comes with the Passover sacrifice to increase the joy of the festival. One must eat all of it in the first two days which are the fourteenth and the fifteenth of Nisan and about this it says “and nothing of the flesh which you offered in the evening should remain on the night of the first day over until the morning.”
Amongst the roots of the commandment: The basis which is fixed for us is concerning the commandment of the topic of Passover, which is a commandment with a strong foundation in our Torah, and therefore we are commanded to make the day of slaughtering it into a day of rejoicing. A person can only truly rejoice with an abundance of meat, and this is why we are commanded not to leave any of the meat which is slaughtered in honour of the joy of Passover over until the third day but rather to eat all of it on the right day to increase happiness on that day and be satiated from joy.
This commandment applies at the time when the Beis Hamikdash stands, to men and to women.