Leviticus 23:7

In the first day ye shall have an holy convocation: ye shall do no servile work therein.

Cross-reference

Leviticus 23:35 applies the same holy convocation and no-work rule to the Feast of Tabernacles, paralleling the structure of this verse.

Numbers 28:18-25 prescribes the offerings and holy convocations for the same feast, reinforcing the command against ordinary work.

Exodus 12:16 gives the original instruction for holy assemblies on the first and seventh days of Unleavened Bread, echoing this verse.