In Super Mario Bros., who informs Mario that the princess is in another castle?

In Super Mario Bros, it is Toad who informs Mario that the princess is in another castle. Throughout the game, Mario encounters Toad in various castles, and each time, Toad tells him that the princess is not present and provides him with a clue about her whereabouts. This recurring interaction between Mario and Toad serves as a plot device, building suspense and urging Mario to continue his quest to rescue Princess Peach.