Psalm 92 (Greek numbering: Psalm 91), known as Mizmor Shir L'yom HaShabbat, is a psalm ostensibly dedicated to the Shabbat day. Though it is permissible to recite it any day, it is generally reserved for Shabbat and is also recited during the morning services on festivals.
According to the Midrash, Psalm 92 was said by Adam. Adam was created on Friday, and he said this psalm on the onset of the Shabbat. It is not a psalm that speaks about the Shabbat, but one that was said on the Shabbat. this was Adam's first day of existence and he marveled at the work of the Creator.