Question: Who has the right to do takfeer of a specific person? Is it permissable for a normal person to do specific takfeer of a person who fell into clear kufr, if he knows the principles of takfeer and its obstacles? Or do we say to him: no, don’t do so, and leave this for the judge, mufti and the followed scholar?

Answer: As you mentioned, the normal person who knows the principles of takfeer and its obstacles has the right to do takfeer.

This is what the we have seen since the time of the Messenger, sallallahu ‘alayhi wa salam, to this age.

As for the one who does not know, then it is not permissable for him, ‘Whoever says to his brother “O Kaafir”, then one of them has fallen into it’.
And takfeer is not from the particulars of the judge, mufti or scholar. It is wrong to believe so.
[Question asked to Shaykh ‘Ali al-Khudayr in as-Salafiyoon Message Board]