ולא תותירו ממנו עד בקר
(שמות יב י)
Do not leave over from the Korban Pesach until the morning of the 15th of Nissan
During the time of the Bais HaMikdash
Males and females.
So we remember the miracles in Egypt, where Hashem made us into royals. Like royals, we don't need to conserve anything for the next day.
If one does it
Then it should be burnt, like something unwanted, like royals do.