Question: It is narrated in a Hadeeth that When the Prophet (peace be upon him) came to Madeenah, he found the Jews observing Sawm (Fast) on `Aashooraa’ (10th of Muharram). So, he observed Sawm during it and ordered that Sawm should be observed in it. How can this be reconciled with his order to act differently from the way of People of the Book in many matters?
Answer: Upon arriving in Madeenah, the Prophet (peace be upon him) used to act like the People of the Book in matters where there was no revelation. Then, Allaah legislated for him to act differently from the way of the People of the Book… read more here.