Sayyed Mohammad Al-Musawi, Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to... Answer updated 3 years ago

Bay’ah is promising to follow and obey. It did happen during the time of pervious prophets like when Easa Jesus (AS) asked people from Bani Israel : Who are my supporters? His disciples  replied: We are the supporters of Allah (3:52). That was just an example of Bay’ah.