Philo Judaeus De Cherubim 90

[90] Since therefore it is naturally the case that things, which are changed, are changed in consequence of fatigue, and since God is subject to no variation and to no change, he must also by nature be free from fatigue, and that, which has no participation in weakness, even though it moves everything, cannot possibly cease to enjoy rest for ever. So that rest is the appropriate attribute of God alone. ¹ 27 And it has been shown that it is suitable to his character to keep festival; sabbaths therefore and festivals belong to the great Cause of all things alone, and absolutely to no man whatever.