Annex to the Convention: Regulations respecting the laws and customs of war on land - Section I : On belligerents - Chapter II : Prisoners of war - Regulations: Art. 9.
Art. 9. Every prisoner of war is bound to give, if he is questioned on the subject, his true name and rank, and if he infringes this rule, he is liable to have the advantages given to prisoners of his class curtailed.