Sahl bin Abdil-llah At-Tustaree rahimahul-llah (died year 283H) was asked:
How can the man know if he is from Ahlus-Sunnah?
He replied: if he realized that he possesses ten* traits:
1-He does not abandon the legion [of Muslims],
2-He does not slander the companions of the prophet peace is upon him,
3-He does not rebel against this Ummah by lifting the sword,
4-He does not reject believing in the predestination,
5-He does not doubt his faith,
6-He does not quarrel in the religion,
7-He does not abandon praying on the sinner of Ahli-Qiblah if he dies,
8-He does not abandon wiping on the socks,
9-He does not abandon praying behind every ruler whether he is an oppressor or just.
*It is nine in total, perhaps one was lost in the chain wal-llahu a’lam. It is also known as the creed of At-Tustaree rahimahul-llah.
Explanation of principles of the belief of Ahlus-Sunnah wal Jamaa’ah by Al-laalakaa’ee 1/182-183