rulling on telling he is not a member of ahlu sunnah is synonymous to calling him kafir
i told one person that he is not a member of ahlu sunnah without actually knowing its meaning what i done is kufr please answer my question fastly
i am very happy to see this site alhamdulillah let allah helps you

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Describing a person that he is not from Ahlus-Sunnah does not necessitate ruling that he is a disbeliever (non-Muslim). Many of those who adhere to Islam are not from Ahlus-Sunnah because they believe in beliefs that are contrary to the methodology of the righteous predecessors . So, they are called Mu’tazillah, or Murji-ah, or Khawaarij, and the like; this does not necessarily mean that they are non-Muslims; rather, they are only misguided innovators.

However, it is not permissible to describe someone with this description until after conclusive evidence has been established on that.

These detailed rulings on the people should be left to the judges and scholars, as they are more insightful in looking at the conditions if they are met in declaring a person as non-Muslim or innovator and looking at the impediments that may prevent calling people as such, based on which they issue the rulings they make.

For more benefit on declaring someone as a non-Muslim, please refer to Fataawa 91677, 87963, 91777, 91372 and 133655.

For more benefit on Ahlus-Sunnah Wal-Jamaa‘ah please refer to Fataawa 2496, 22613, 33503, and 351652.

Allah Knows best.