וַיַּ֨עַשׂ יֹאשִׁיָּ֧הוּ בִֽירוּשָׁלִַ֛ם פֶּ֖סַח לַיהוָ֑ה וַיִּשְׁחֲט֣וּ הַפֶּ֔סַח בְּאַרְבָּעָ֥ה עָשָׂ֖ר לַחֹ֥דֶשׁ הָרִאשֽׁוֹן׃
And Josiah kept a passover unto the LORD in Jerusalem; and they killed the passover lamb on the fourteenth day of the first month.
Read halakhic rulings (Jewish law) on II Chronicles 35:1: and classical halakhic sources.