Halakhah su Deuteronomio 16:4

I also found explicit with regard to the first of the holidays (Passover), which God gave to Israel prior to instructing them about the Sabbath, “on the fourteenth day of the month at evening you should eat unleavened bread, until the twenty first day of the month at evening” (Exodus 12:18), a total of “seven days” (ibid. 12:19). Thus the evening of the fifteenth is the first day. It is also written “[neither shall any of the flesh] from which you offered in the evening of the first day [be left over] until the morning” (Deuteronomy 16:4). Also, it is known that the firstborn were smitten at midnight (Exodus 12:29), yet it is written “on the day that I smote all firstborn” (Numbers 3:13, 8:17).⁴ The verse informs us that God sanctified all Jewish first born on the day that the Egyptian first born were slain. It seems likely that this took place on the first day of Passover. Also in Scripture “this day is a day of tidings…if we wait until the morning light” (2 Kings 7:9).

To not leave over from the festive (chagigah) sacrifice to the third day: To not leave over anything from the festive sacrifice of the fourteenth day until the third day - and that is the sacrifice that comes with the Pesach [sacrifice] to increase the joy - but rather to eat it all within two days, which are are the fourteenth and fifteenth. And about this is it stated (Deuteronomy 16:4), "and none of the meat of what you slaughter on the evening of the first day shall be left to the morning." And the received (traditional) understanding came upon this (Pesachim 71a) that the verse is speaking about the festive [sacrifice] that comes with the Pesach, [to say] that the time of its eating is up to two days. And about this festive [sacrifice], Scripture stated (Deuteronomy 16:2), "And you shall slaughter the Pesach to the Lord, your God, flock and cattle" - meaning to say, that with the Pesach, he bring another sacrifice; meaning to increase the joy.