"We are shocked at the Quetta terrorist attack and we stand with the bereaved families," Xinhua news agency quoted Hussain as saying during the country's Independence Day celebration.
A suicide bomber killed 74 people in a Quetta hospital on August 8.
"Every Pakistani feels the pain," the President said. "The blood of the innocent people will not go waste.
"I announce here, the government will take revenge for the blood of the innocent people."
The Islamic State and a Pakistani Taliban group claimed responsibility for the suicide attack. Most victims were lawyers.
"Every visible and invisible enemy will be chased and crushed in order to establish durable peace in the country," said the President.
He said the menace of terrorism would be eliminated from the country with decisive actions and renewed determination.
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