Règle correspondante
Spain
Practice Relating to Rule 87. Humane Treatment
Section D. Persons deprived of their liberty
Spain’s LOAC Manual (1996) provides that captured enemy combatants, those who surrender and prisoners of war must be respected and treated with humanity. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Publicación OR7-004, 2 Tomos, aprobado por el Estado Mayor del Ejército, Division de Operaciones, 18 March 1996, Vol. I, §§ 7.3.a.(7), 8.4.a.(1), 10.6.b.(2), 10.6.c. and 10.8.f.(2).
Spain’s LOAC Manual (2007) states: “In international conflicts, unlawful combatants … and persons whose status is in doubt must be treated with humanity and respect when they are captured, in the same way as lawful combatants.” 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 5.5.b; see also § 7.3.a.(7).
The manual also states that prisoners of war “must be treated humanely”. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 8.4.a.(1); see also § 10.3.e.(1).
The manual further states with regard to combatants without prisoner-of-war status:
They should be given the chance to surrender and, once hors de combat, must be treated humanely. No acts of violence must be committed against them unless they carry out a hostile act or attempt to escape. … What is important is that they treat them with humanity and respect once they are hors de combat. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 7.3.a.(8).
Spain’s Royal Ordinances for the Armed Forces (2009) states that members of the armed forces “[m]ust treat … prisoners [and] detainees … that are in their power … humanely.” 
Spain, Royal Ordinances for the Armed Forces, 2009, Article 107; see also Article 110.
In 2010, in its report to the UN General Assembly on the status of the 1977 Additional Protocols, Spain stated:
Article 85 entitled “Principle of Humanity”, contained in Title IV on Operations [of the Royal Ordinances for the Armed Forces (2009)] clearly embodies the spirit of the [1949] Geneva Convention and its [1977] Additional Protocols, as it provides that “[the] … conduct [of members of the armed forces] in any conflict or military operation must conform to the applicable rules of the international treaties on international humanitarian law to which Spain is a party”.
That is further developed in Chapter VI on Ethics in Operations, which goes into specific duties under international humanitarian law … the protection of … prisoners, [and] detainees. 
Spain, Report on the Status of the Protocols Additional to the Geneva Conventions of 1949 and relating to the protection of victims of armed conflict, 5 May 2010, Section 2.