What is the Shar'i (Islamic legal) stance regarding followers of the Ash'ari creed who describe those who love Shaykhs Ibn Baz and Ibn 'Uthaymeen as "chickens" and consider the people of Athar (narrations/traditions) to be anthropomorphists (Mujassimah)? And is it permissible to boycott them and not accept their invitations?

Insults and mockery are only committed by those far from religion, and their perpetrator resembles criminals who mock believers. The fundamental principle in responding to opponents is with evidence and proof, not with insults and mockery, as Allah Almighty says: (Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best). As for shunning a Muslim, it is forbidden for more than three days, but shunning people of religious innovation and heresies is permissible if a legitimate benefit results from it, such as the innovator recanting or reducing the spread of their innovation.