Deception in war
Question

                Does Islam permit deception in war? Is this considered to be betrayal and treachery?
Praise be to Allah.Allaah has forbidden treachery and has condemned those who do it. Allaah says (interpretation of the meaning): 
“They are those with whom you made a covenant, but they break their covenant every time and they do not fear Allaah”
[al-Anfaal  8:56]
And the Prophet (peace and blessings of Allaah be upon him) said: “Every betrayer will have a banner on the Day of Resurrection, by which he will be known.” (Narrated by al-Bukhaari, 6966; Muslim, 1736)
 Al-Bukhaari narrated that Ibn ‘Umar (may Allaah be pleased with him) said: ‘The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘There are four characteristics, whoever has them all is a pure hypocrite: when he speaks, he lies; when he makes a promise he breaks it; when he is entrusted with something he betrays that trust; and when he argues, he speaks in an obscene manner. Whoever has one of these traits has a trait of hypocrisy until he gives it up.” (Narrated by al-Bukhaari, 3878; Muslim, 58)
 And it was narrated that Maalik said: “I heard that ‘Abd-Allaah ibn ‘Abbaas said: ‘There is no people who betrays their covenant but Allaah gives their enemies power over them.” (al-Muwatta’, Baab ma jaa’a fi’l-wafa’ bi’l-‘ahd)
 Yet despite this condemnation of betrayal, Islam allows deception in war in order to attain victory. Al-Nawawi said: “The scholars are agreed that it is permissible to deceive the kuffaar in war in any way possible, except if that would mean breaking the terms of a treaty or trust, in which case it is not permitted.
 The Prophet (peace and blessings of Allaah be upon him) said: “War is deceit.” (Narrated by al-Bukhaari, 3029; Muslim, 58).  One of the most dangerous elements of deceit is taking the enemy by surprise and catching them unawares before they can get ready to fight. When the Messenger (peace and blessings of Allaah be upon him) wanted to head for Makkah in order to conquer it, he ordered the Muslims to get ready without telling anyone of his intention until after they had set out for Makkah, and after taking all precautions to prevent news of that reaching the mushrikeen.
And the Prophet (peace and blessings of Allaah be upon him) used to send out many raiding parties, and he would tell them to travel by night and conceal themselves by day so that they could catch the enemy unawares.
 Although it is permissible to use deception in war, we say that Islam has attained a high standard of ethics with regard to the use of these tricks in war. Among the most prominent examples of that are the following: 
‘Umar ibn al-Khattaab wrote to the commander of an army that he had sent out: “I have heard that some men among you look for kaafirs, then when they run to hide in difficult mountainous terrain they say, ‘Do not be afraid,’ then when they catch up with them they kill them. By the one in whose hand is my soul, if I hear that anyone has done that I will chop off his head.”
 It was narrated that Abu Muslimah said: “ ‘Umar ibn al-Khattaab said: ‘By the One in Whose hand is my soul, if any one of you were to point to the sky [i.e., a gesture to imply that he will not harm him] to make a mushrik come down to him and then kill him, I would kill him for that.’”
 Islam has forbidden treachery, and treachery is not one of the kinds of tricks and deception that are permitted in war.
 This Islamic sharee’ah makes a distinction between the kinds of deceit that are permitted and that which involves treachery and breaks treaties.
 See al-‘Allaaqaat al-Khaarijiyyah fi Dawlat al-Khilaafah, 197.