«إِنْ عَمَلْتْ خِيرْ النُّومْ أَخْيَرْ»

The saying sets two things against each other, a good deed and sleep, and ranks sleep as the better of the two. The surprise lies in placing a plain bodily need above something normally counted as praiseworthy.

As a remark, it marks a particular situation as one in which sleep is the preferable choice. It delivers that judgment by declaring that, in such a case, nothing done, however good, would outrank simply sleeping.

Fits as a comment on a situation the speaker regards as one where sleep is the better option, stating that preference by ranking sleep above even a good deed.