Those who abstain from Takfeer and warn from that...

Question: As-salamu �alaykum wa rahmatullahi wa barakatuhu our
noble Shaykh; What are the guidelines of Takfeer? And who has the right
to perform Takfeer upon a specific individual? And do the laymen have the
right to make Takfeer upon whoever insults the Messenger or allies with
the kuffaar, whether he was ignorant or knowledgeable? And what is your
opinion regarding those who abstain