Sh'mot (Exo) 12:26-27

When your children ask you, ‘What do you mean by this ceremony?’ say, ‘It is the sacrifice of ADONAI’s Pesach [Passover], because [ADONAI] passed over the houses of the people of Isra’el in Egypt, when he killed the Egyptians but spared our houses.’” The people of Isra’el bowed their heads and worshipped.