The fifth imam of the school of the Ahlul Bayt, Imam Muhammad al-Baqir once told his student by the name of Jabir, “Is it enough for a person to embellish himself as our Shi'a (follower) by professing love for us, the Ahlul Bayt? Nay! By Allah, a person is not our follower unless he fears Allah and obeys Him. Our followers are only recognized, O Jabir, by their humility, submission, honesty, abundant praise of Allah, fasting, prayers, goodness to their parents, attention to the poor, needy, debtors, and orphans living nearby, speaking of the truth, recitation of the Quran, holding back their tongues except for good words, and trustworthiness towards one's relatives in all affairs.”
“Shi'a” means a group of followers and it occurs in the Quran many times in reference to the followers of the previous prophets, such as Prophet Ibrahim (Abraham) and Prophet Musa (Moses). Shi'a today refers to the followers of a particular school of Islamic thought, which is based on the teachings of the Prophet and his family, and sometimes it is referred to as the “school of Ahlul Bayt” (the family of the Prophet). While no schools of thought existed at the time of the Prophet Muhammad, he still used to refer to a certain group of people as the “Shi'a of Ali.”
Some narrations in which the Prophet Muhammad used the term “Shi'a of Ali” are as follows:
We were gathering around the Prophet when Ali ibn Abi Talib came. He said, 'Verily, my brother has come to you,' and he placed his hand on the Ka΄bah and said, 'By the One Who holds my soul in His hand, this man and his Shi'a will indeed be the successful ones on the Day of Judgment.' (Narrated by Jabir ibn 'Abdillah al-Ansari)
The Prophet of Allah was with me when his daughter Lady Fatima came to greet him with her husband Ali. The Prophet of Allah raised his head and said, 'Be happy Ali; you and your Shi'a will be in Paradise.' (Narrated by Um Salamah, the wife of the Prophet Muhammad)
As these narrations show, the Prophet Muhammad himself was in fact, the first person to use the term “Shi'a,” and what's more is that he always used the term in reference to Imam Ali. After the Prophet passed away those who were loyal to Imam Ali were also known as the Shi'a. During the second century Hijrah (i.e., two centuries after the migration of the Prophet Muhammad from the city of Makkah to the city of Madina—the event which marks the beginning of the Islamic calendar), the Abbasid caliphs officially patronized the four Sunni schools of thought which were popularized by the enthusiasm of some of their leaders. As for the Shi'a, after the assassination of Imam Ali, they followed the leadership of his son Hassan, and after him his brother Husayn, and the subsequent nine imams who were the descendants of Husayn. They followed them on the firm basis of evidence in the Noble Quran and the tradition of Prophet Muhammad who explicitly repeated on many occasions that he [the Prophet] would be followed by twelve imams and that they would all be from the tribe of Quraysh.
Therefore, Shi'ism can be termed as the following of the Noble Quran and the tradition of Prophet Muhammad as conveyed by his family, whom he appointed (i.e., the Ahlul Bayt). After the Prophet Muhammad, the Shi'a followed the twelve divinely ordained imams as successors of the Prophet Muhammad, as will be seen in the subsequent sections.
 al-Kulayni, al-Kafi, Vol. 2, 74
 Noble Quran, 28.15
 Ibn Hajar, Lisan al-Mizan, Vol. 2, 354
 Tawzih al-Dala΄il fiTashih al-Fada΄il, 505
 Ibid., 507
 Ibn Asakir, “The History of the City of Damascus” Section: Biography of Imam Ali
 Sahih al-Bukhari; Sahih Muslim, Vol. 2, 191; Sahih al-Tirmidhi, Vol. 2, 45; Musnad Ahmad ibn Hanbal, Vol. 5, 106; Sunan Abu Dawud, Vol. 2, 207