Buhari has missed three consecutive Cabinet meetings in Nigeria, prompting concerns for his health.
Minutes later, the 74-year-old Buhari startled Africa's most populous nation with the news of his departure.
Photos tweeted by the president show dozens of the freed girls at Buhari's official residence.
In a statement issued yesterday by APC National Publicity Secretary, Mallam Bolaji Abdullahi, the party described the feat as yet another evidence that President Buhari is fulfilling his promises. "He promised that the presidency will personally supervise their rehabilitation".
This comes following negotiations between the Islamist military group and the Nigerian government, the president's office has said. In May 2014 we were to receive these girls, we had already committed every resources available, logistics were made but when we got to the negotiating point, the International Red Cross, myself and some lady doctors from SSS, we were disappointed. A handful of other girls have either escaped or been rescued, but 113 still remained unaccounted for following Saturday's release.
"Welcome our girls, welcome our sisters", Kyari said to the girls, who sat quietly in chairs. "Their life in captivity has been one that depicts suffering, it depicts the fact that they have been starved, abused, and as we have seen before some of those girls have come back with children, and some of them have also come back with news of how they have been sexually abused".
The mass abduction of the 276 girls exposed the mounting threat posed by the Daesh-linked fighters.
"We will help reunite the girls with their families and make sure they can continue their education in a safe environment".
"It is a good development, coming, timely, before emotional trauma sends the parents of these girls to their early graves".
Human rights advocates also fear some of the girls have been used by Boko Haram to carry out suicide bombings as part of the group's insurgency.
The audacious kidnapping brought the insurgency to world attention, triggering global outrage that galvanised support from the former USA first lady Michelle Obama and Hollywood stars. The failure of Nigeria's former government to act quickly to free the girls sparked a global Bring Back Our Girls movement; USA first lady Michelle Obama posted a photo with its logo on social media.
The abduction drew global concern with various celebrities such as former First Lady Michelle Obama, Beyonce and Salma Hayek spearheading a campaign called "Bring Back Our Girls". At the meeting, the president welcomed the girls in the capital city of Abuja and said: "I can not express in a few words how happy I am to welcome our dear girls back to freedom".
Boko Haram, which previous year pledged loyalty to Islamic State, has kidnapped hundreds of men, women and children in its campaign to carve out a medieval Islamist caliphate.
He stressed that although it could not be categorically stated how many factions there are, there is definitely more than one faction of the insurgent group.