question #1 Sahih Muslim 135b, Book 1, Hadith 255 : What is the significance of affirming the truthfulness of Allah and His Messenger in Islamic teachings?

The people will constantly, and the rest of the hadith is the same as that transmitted by ‘Abdul-Warith with the exception that there is no mention of the Messenger of Allah in that, but he observed at the end of the hadith: Allah and His Messenger told the truth.