Rashi on Exodus 20:9/רש"י על שמות כ׳:ט׳

1ועשית כל מלאכתך [SIX DAYS SHALT THOU LABOUR] AND DO ALL THY WORK — When the Sabbath comes it should be in thy eyes as though all thy work were done (completed), so that thou shouldst not think at all about work (Mekhilta).