Exodus 12:1-4 New Revised Standard Version (NRSV)
The First Passover Instituted
12 The Lord said to Moses and Aaron in the land of Egypt: 2 This month shall mark for you the beginning of months; it shall be the first month of the year for you. 3 Tell the whole congregation of Israel that on the tenth of this month they are to take a lamb for each family, a lamb for each household. 4 If a household is too small for a whole lamb, it shall join its closest neighbor in obtaining one; the lamb shall be divided in proportion to the number of people who eat of it.