AnswerBefore going into the details below, it is important to point out that Both Sunnis and Shiites are Muslims. They both believe in one and only one God and believe in his prophet and Messenger Muhammad. They believe in Quran and in the five pillars of
Islam. They pray facing the same direction (Kaaba). They may pray together in the same mosque and led by a Sunni or Shiite at no difference.
However, the Sabean Mandeans are by all means not Muslims. They are considered by Muslims as unbelievers.
Details
Mandaean beliefs maybe summed up as follows:
-Beliefs-
The Mandaean religion is Gnostic and quite strictly dualistic in nature. For the Mandaeans there exists a clearer division between light and darkness. The ruler of darkness is called Ptahil (similar to the Gnostic Demiurge), and the originator of the light (i.e. God) is only known as "the great first Life from the worlds of light, the sublime one that stands above all works".
Mandaeans consider Abraham, Moses, Jesus, and Muhammad to be false prophets. For them the greatest of prophets is John the Baptist. According to Mandaean dogma, Mandaeanism was the original religion of Adam. They have a hierarchical clergy, they practice frequent baptism, and hold public worship on Sundays. They deplore fasting and monasticism, and believe in peace above all.-Scriptures-
There are many Mandaean scriptures, the most important being the Ginza Rba, a collection of history, theology, and prayers.
The Ginza Rba consists of 18 books in 62 chapters containing about 700 pages. The book, still mainly hand written, with upright text on each right-hand page for the living and text when turned upside-down is the left for the dead. The right section of the Ginza Rba contains sections dealing with theology, creation, ethics, historical, and mythical narratives. The left section of Ginza Rba deals with man's soul in the after life.
Sources:
http:/www.spiritus-temporis.com/mandaeanism/mandaean-beliefs.html
http:/www.spiritus-temporis.com/ginza-rba
-Shi'ite Islam-
The Shi'ites are the smaller of the two main group of Islam. There are a number of subdivisions under the 'umbrella' of 'Shi'a' and although they differ in the details all of them believe that only the heirs of the fourth caliph, Ali, are the legitimate successors of Muhammad.
The Shi'ites call these successors Imams. Shi'ites do not accept that the Imam is to be only a political leader but they believe that they are literally 'manifestations of God', they are sinless, infallible and the bringers of true understanding to all humanity. They are referred to within the Shi'ite tradition as being masum, that is, free from error or sin.
The last Imam, the Mahdi, is believed not to have died but to be in hiding and Shi'ites believe that he will appear at the end of time in order to bring about the victory of the Shi'a faith (see third paragraph below).
The main groups under the Shi'ite umbrella are the Zaydiyyah or Fivers, the Isma'iliyyah or Seveners and the Imamiyyah or Twelvers. The numbers five, seven and twelve refer to the last authorised interpreter of the law or Imam that each group accepts. Of the three the Twelvers are the biggest & it was in 931 that the Twelfth Imam disappeared.
This was a seminal event in the history of these Shi'ite Muslims. According to R. Scott Appleby, a professor of history at the
University of Notre Dame,
"Shi'ite Muslims, who are concentrated in Iran, Iraq, and Lebanon, [believe they] had suffered the loss of divinely guided political leadership" at the time of the Imam's disappearance. Not "until the ascendancy of Ayatollah Ruhollah Khomeini in 1978" did they believe that they had once again begun to live under the authority of a legitimate religious figure.
The other important concept in Shi'ite Islam concerning the Imam (regardless of whether he was the Fifth, the Seventh or the Twelfth) is that he will return. He is called the Mahdi and will bring about the Kingdom of God on earth after an apocalyptic battle between the forces of Islam and the rest of the world. [Note that other groups descended from Shi'ia Islam such as the Babis and Baha'is define the 'battle at the end of time' as a symbolic or metaphysical one rather than an actual battle.]
A useful site for information on the various groups is the Overview of World Religions site hosted by St Martin's College in the UK.
http:/philtar.ucsm.acz.uk/encyclopedia/islam/shia/index.html
-Sunni Islam-
The largest group, called the Sunnis believe that the first four caliphs--Muhammed's successors--rightfully took his place as the leaders of Islam. They recognize the heirs of the four caliphs as legitimate religious leaders. These heirs ruled continuously in the Arab world until the break-up of the Ottoman Empire following the end of the First World War.
There are four main schools of jurisprudence in Sunni Islam, these are Hanbali, Maliki, Hanafi and Shafi'i.