ANNEX TO THE CONVENTION : Regulations respecting the laws and customs of war on land #Section II : On hostilities #Chapter V : On armistices - Art. 36.
Art. 36. An armistice suspends military operations by mutual agreement between the belligerent parties. If its duration is not fixed, the belligerent parties can resume operations at any time, provided always the enemy is warned within the time agreed upon, in accordance with the terms of the armistice.