John 11:55

This is the third and final Passover that John mentioned in his Gospel (cf. John 2:13; John 6:4) and probably the fourth one during Jesus’ public ministry. John mentioned the first, third, and fourth of these. [Note: Hoehner, p. 143.] The Mosaic Law required that the Jews who had become ritually unclean had to purify themselves for one week before participating in this feast (Numbers 9:6-14). Therefore many of them went to Jerusalem at least one week before the feast began to undergo purification.