At least 83 more were injured as the clerics met at the Uranus hall to mark the birthday of the Prophet Muhammad.
It is one of the deadliest attacks in Kabul in recent months.
No-one has admitted responsibility for the blast, but the Islamic State group has said it was behind most of the recent deadliest attacks.
Continuing attacks by the Taliban have also stepped up pressure on security forces.
At least 1,000 people were in the hall at the time of the explosion, Tolo News quoted eyewitnesses as saying.
1TV News quoted the health ministry as saying that 24 of the wounded are severely injured.
A manager at the hall said the suicide bomber blew himself up in the middle of the gathering.
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