Related Rule
Germany
Practice Relating to Rule 140. The Principle of Reciprocity
Germany’s Military Manual (1992) states:
People complying with the provisions of international humanitarian law themselves can expect the adversary to observe the dictates of humanity in an armed conflict. No one shall be guided by the suspicion that soldiers of the other party to the conflict might not observe the rules. Soldiers must treat their opponents in the same manner as they themselves want to be treated. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten – Handbuch, August 1992, § 1204.
Germany’s IHL Manual (1996) notes: “Only those who respect themselves the regulations of international humanitarian law may expect that the adversary also respects them (so-called principle of reciprocity).” 
Germany, ZDv 15/1, Humanitäres Völkerrecht in bewaffneten Konflikten – Grundsätze, DSK VV230120023, Bundesministerium der Verteidigung, June 1996, § 109.
In 2005, in its Seventh Human Rights Policy Report submitted to the Bundestag (Lower House of Parliament), Germany’s Federal Government stated:
At the 28th International Conference of the Red Cross and Red Crescent in Geneva in December 2003, the then Federal Government Commissioner for Human Rights Policy and Humanitarian Aid at the Federal Foreign Office, Claudia Roth, stated the following with regard to the treatment of prisoners of war in Guantánamo:
“International humanitarian law and the international human rights protection standards create legal protection, without gaps, for the individual human being. No grey areas can be allowed in this comprehensive protective mechanism, to which States have committed themselves.
This applies to prisoners of war, suspects and also to a war criminal, who, rightly so, is held to account. He also is entitled to humane treatment and a fair trial, in accordance with the rule of law.
Also in the fight against terrorism we must remain committed to our humanitarian standards, even if the adversary has disregarded them in a cruel and unscrupulous way. I would like to stress this expressly with a view to the detainees in Guantánamo.” 
Germany, Federal Government, Seventh Human Rights Policy Report, 17 June 2005, p. 25.