After the Glorious Qur’an, the most important source for understanding Islam and therefore Shi‘i thought is the Sunnah of the Prophet Muhammad, including his sayings and his deeds. The Qur’an itself grants this high position to the Prophet, as he is referred to as the one who is responsible for explaining the Qur’an (16:44) and teaching the Qur’an and wisdom (62:2). The Prophet is a perfect example for the believers (33:21). He never speaks out of his own wishes (53:3). Muslims are asked to hold on to whatever he gives them and refrain from whatever he prohibits (59:7).
Knowing the above verses and many other verses regarding the status of the Prophet, and taking into account the significance of being a divine messenger chosen directly by God and spoken to by Him, the Shi‘a, along with other Muslims, cultivated a state of sincere love for and devotion to the Prophet Muhammad.
Discovering Shi’i Islam Mohammad Ali Shomali 9th edition