On Shabbos we say Psalm 92. Although this Psalm does not directly mention Shabbos, the commentators offer reasons why it is recited on this day. The Radak mentions that Praising G-d is difficult during the weekdays because people are hard at work to make a living. On Shabbos, though, when no work is done, people are free to focus on praising G-d, which is a main topic discussed in this Psalm.