Where the story is told
The main account is in Surah al-A'raf, Quran 7:163-166. Allah tells the Prophet ﷺ to ask the Children of Israel about the town that was by the sea. It is also mentioned briefly in Quran 2:65-66, and in 4:47 and 5:60.
The Sabbath was a day the Children of Israel were commanded to keep, and the Quran also mentions a command given to them not to transgress in it (4:154). The Quran describes this story as a lesson for those who heard it then and for those who came after.