וַיַּעֲמִידֵ֣ם לָעַ֣ד לְעוֹלָ֑ם חָק־נָ֝תַ֗ן וְלֹ֣א יַעֲבֽוֹר׃
Y las hizo ser para siempre por los siglos; Púso les ley que no será quebrantada.
Rashi on Psalms
He issued a decree to them, that this one should serve by day and that one should serve by night. which will not change That decree.