What is Sunnis?
Islam has different branches, including Sunnism. This movement is also known as the largest group in Islam. It consists of Sunni Muslims who strictly follow the path of the Prophet and his Companions. The word 'Sunnah' means tradition, and Sunnism refers to the Prophetic traditions.
What do Sunnis believe?
They believe in the orthodox methodology of Islam and thus are strict followers of what the Prophet and his companions believed. Sunnis choose the middle way of all sects in Islam.
The difference between Sunnis and all other sects is that they follow the Companions. They are strict about it and turn in beliefs directly to how it was originally conveyed.
Sunnism is also known as Ahlu Sunnah. The saved group of Islam, Ahlu Sunnah, is a group that clings to the original methodologies.
'Abdullah ibn 'Amr reported:
that the Messenger of Allah (ﷺ) said: “The Benu Israel split into 72 groups, and my Ummah will split into 73 groups. They are all in the fire except one.” He (Abdullah bin 'Amr) asked: “And which one is that O Messenger of Allah?" He (ﷺ) said: "Whoever follows me and my companions."
Sunan Tirmidhi 2641
Who are Sunni?
There are different groups that claim to be Sunni, but in reality they believe differently from what the Prophet and his companions believed.
The Prophet gave a criteria to know who is actually on the right path. So these criteria determine who is a Sunni. The Muslims are ordered to follow the path of the Salaf Saliheen (pious predecessors). The pious predecessors are all Muslim scholars of the golden ages.
The Salaf Saliheen are the Companions, students of the Companions, and the students of those students. These three generations of scholars are on the correct path, and Muslims are therefore commanded to follow them.
Ibn 'Umar reported:
"Umar ibn Khattab gave us a Khutbah (sermon) in Al-Jabiyah. He said: 'O people! I have indeed stood among you as the Messenger of Allah stood among us, and the Prophet said: 'I command you to hold fast to my companions, then those who come after them, then those who come after them."
Sunan Tirmidhi 2165
Difference between Sunnism and Shiism
The difference lies mainly in the doctrine of faith. Shiites believe that 'Ali (nephew of the Prophet) should have been the first Khalif. The Sunnis believe that Abu Bakr (companion of the Prophet) was chosen as Khalif and had therefore more right over it.
Shia started with the quarrel between 'Ali and a companion named Mu'awiyyah. From this, a group took the side of 'Ali (original Shi'ites) and a group took the side of Mu'awiyyah.