It appears likely, unless the Taliban spokesman is lying, that this is the work of the Islamic State, which targeted the Ulema Council for not accepting its authority as the caliphate, thus rendering itself apostate, and thus lawfully killed.
“Toll In Afghan Attack Climbs To 55, Taliban Denies Responsibility, RFE/RL, November 21, 2018:
Afghan authorities are working to identify those responsible for a suicide bombing that killed at least 55 people and wounded scores more who were attending a religious gathering in Kabul.
The victims included religious scholars from all over Afghanistan, invited by the Ulema Council to celebrate the birth anniversary of Prophet Muhammad on November 20.
“As of now we don’t know which militant organization could be behind the attack. Investigations are at a preliminary stage,” a senior investigator who was at the site said on November 21.
The Ulema Council, the country’s largest religious organization, brought together scholars from the Sunni sect.
Though Sunni themselves, Taliban and Islamic State fighters have targeted religious scholars aligned with the Afghan government in the past.
But the Taliban quickly denied any involvement, and spokesman Zabihullah Mujahid said late on November 20 that his group condemned any attack on civilians or religious clerics….