Wa`alaykum As-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear questioner, thank you very much for having confidence in us, and we hope our efforts, which are purely for Allah's Sake, meet your expectations.
First of all, it is to be noted that Islam prohibits torturing living people and mutilating the dead, even if they are non-Muslims.
Responding to the question, Sheikh Faysal Mawlawi, Deputy Chairman of the European Council for Fatwa and Research, states the following:
First, it is not allowable to torture the living or mutilate the dead, even if they are non-Muslims. In the hadith of the Prophet (peace and blessings be upon him), when he was sending Hamzah Al-Aslami on an expedition, he instructed him saying: "If you find so-and-so, kill him. But never kill him by burning, for none uses fire in torturing except the One Who created it (i.e., Allah)." (Reported by Abu Dawud)
In another hadith, Safwan ibn `Assal said: The Prophet (peace and blessings be upon him) sent us on an expedition and said: “Move under the protection of Allah and for the sake of Allah. Fight those who disbelieve in Allah but never mutilate (the dead).” (Reported by Ibn Majah)
Second, it is permissible to mutilate the dead only in case of retaliation. If anyone cuts the ear of another, his ear is to be cut in return. If he inflicts any physical damage on anyone, he should be retaliated against in the same manner. In case of war, Muslim are allowed to take vengeance for their mutilated dead mujahids (fighters) in the same way it was done to them. Almighty Allah says: (If ye punish, then punish with the like of that wherewith ye were afflicted. But if ye endure patiently, verily it is better for the patient.) (An-Nahl 16: 126)
This verse was revealed when the polytheists mutilated the corpse of Hamzah ibn `Abd Al-Muttalib (may Allah be pleased with him). The Prophet (peace and blessings be upon him) swore to mutilate seventy corpses of the polytheists in retaliation for what they had done with Hamzah's body. Hence, this verse was revealed to indicate that punishment should be done in the same manner without any sort of transgression, so that the Prophet (peace and blessings be upon him) was permitted to mutilate only one corpse of the polytheists. However, the verse also shows that patience and refraining from retaliation are better in Allah's Sight. Thereupon, the Prophet (peace and blessings be upon him) refrained from it and did not mutilate anybody.
Moreover, Dr. Ahmad Abu-Al-Wafa, Professor of International Law, Faculty of Law at Cairo University, adds:
Mutilating the corpses of the dead is prohibited in man-made international law. It considers it a war crime for which severe penalty is due.
As far as Islamic Shari`ah is concerned, two main points should be stressed:
1. Mutilating corpses is prohibited in the same way torturing the living is forbidden.
2. It is better not to reply to the evil acts of the enemy in the same manner, except if responding in the same way will deter the enemy from exceeding their limits by mutilating corpses. Almighty Allah says: (If ye punish, then punish with the like of that wherewith ye were afflicted. But if ye endure patiently, verily it is better for the patient) (An-Nahl 16: 126) and (The guerdon of an ill-deed is an ill the like thereof. But whosoever pardoneth and amendeth, his wage is the affair of Allah. Lo! He loveth not wrong-doers.) (Ash-Shura 42: 40)
Finally, Sheikh `Ikrimah Sabri, the former Mufti of Al-Quds (Jerusalem) and Khateeb of Al-Aqsa Mosque, concludes:
In fact, the principle of reciprocity has well-established rules in Shari`ah, whereby Muslims are warned against embarking on such inhumane attitudes. For instance, if the enemy mutilates the dead bodies of Muslims, the Muslim army is not permitted to act in the same manner.
In all cases, Muslims should not initiate the aggression, for Islam is the religion of mercy. War is not the first option in the life of Muslims; rather, it comes after da`wah (call to Islam) and kind advice.
You can listen to the Friday Sermon delivered by Dr. Maher Hathout, at the Islamic Center of Southern California, US, titled: Mutilation of Dead Bodies from an Islamic Perspective, on April 2, 2004 Safar 12, 1425.