Leviticus 23:3-6

³six days is work done, and in the seventh day is a sabbath of rest, a holy convocation; ye do no work; it is a sabbath to Jehovah in all your dwellings.

⁴'These are appointed seasons of Jehovah, holy convocations, which ye proclaim in their appointed seasons:

⁵in the first month, on the fourteenth of the month, between the evenings, is the passover to Jehovah;

⁶and on the fifteenth day of this month is the feast of unleavened things to Jehovah; seven days unleavened things ye do eat;