It follows a car bomb attack on Saturday in Benghazi which killed three UN staff.
The truce involves the UN-backed Government of National Accord and the rogue general, Khalifa Haftar.
His forces have been attacking the capital, Tripoli, since April. More than 1,000 people have died, according to the World Health Organization.
Gen Haftar agreed to the truce “so that Libyan citizens can celebrate this Eid in peace”, his spokesman Ahmad al-Mesmari explained.
The truce started on Saturday at 15:00 local time (13:00 GMT) and would last until the same time on Monday afternoon, the spokesman added.
Eid al-Adha is the Muslim festival which commemorates when God appeared to Ibrahim in a dream and told him to sacrifice his son but before the sacrifice goes ahead, God provides a lamb to be sacrificed instead.
The festival happens after the Hajj – the annual pilgrimage to the holy city of Mecca in Saudi Arabia.