Charles Ellicott Commentary Psalms 122:4

"Whither the tribes go up, even the tribes of Jehovah, [For] an ordinance for Israel, To give thanks unto the name of Jehovah." — Psalms 122:4 (ASV)

Unto the testimony. —This is erroneous. The words are parenthetical: There go (or, must and shall go) the tribes, the tribes of Judah (it is an ordinance for Israel) to praise the name of Jehovah. (Deuteronomy 16:16, regarding this regulation.)