What caused the earliest disagreement between groups that would become Shia and Sunni Muslims

Brandy has been given a great deal of opportunity to advance her career. she recently got a huge increase in authority and salary, and she was hired to do what she has always claimed was her dream job. however, brandy is not enthusiastic about coming to work, and when she is there, she spends most of her time complaining about how maurice got a bigger office and nicer furniture than she did. brandy’s behavior would seem to support theory.