Charles Ellicott Commentary Numbers 9:12

"they shall leave none of it unto the morning, nor break a bone thereof: according to all the statute of the passover they shall keep it." — Numbers 9:12 (ASV)

According to all the ordinances. —The word rendered ordinances is in the singular number: according to all the ordinance (or statute). The primary reference is probably to the law respecting the Paschal Lamb. According to Jewish tradition the feast was only observed for one day instead of seven, and it was not necessary to put away leaven.