Not only is it prohibited to perform labor on Shabbat, but at times even discussing future plans to perform labor after the conclusion of Shabbat is prohibited. By contrast, it is not prohibited to think about doing labor after Shabbat. The Sages relate a story about a man who adopted a stringency and refrained from performing labor about which he had merely thought about on Shabbat.

There was an incident involving a certain pious individual who went out for a stroll in his vineyard on Shabbat, and he saw there a certain breach in a fence and thought to repair the fence at the conclusion of Shabbat. He said: Since I thought to repair the fence, I will never repair the fence. What did the Holy One, blessed be He, do for him? He arranged for a branch of a caper bush to grow into the breach and repair the fence. All his days, he sustained himself and earned his living from the fruits of the caper bush. (Jerusalem Talmud, Shabbat 15:3)