Some acts are forbidden on the Sabbath even though they neither resemble nor lead to prohibition work. Why then were they forbidden? Because it is written: “If you refrain from following your business on the Sabbath, on my holy day. If you honor it, not following your wonted ways, not pursuing your business, nor speaking of it Issiah, 58:13). Hence, one is forbidden to go anywhere on the Sabbath in connection with his business, or even to talk about it. One must not discuss what to sell or what to buy etc. hat is to say, speaking of business on the Sabbath is forbidden; thinking of it, however, is permitted.
Mimonides, (Yad Hazakah) Mishneh Torah, Sabbat, Chapter 24 Halacha 1 pg 71