آداب الجهاد
Abu Hurairah and Jābir (may Allah be pleased with both of them) reported that the Prophet (may Allah's peace and blessings be upon him) said: "War is deception."
عن أبي هريرة وجابر -رضي الله عنهما-: أن النبي -صلى الله عليه وسلم- قال: «الحَرْبُ خَدْعَة».
شرح الحديث :
This Hadīth indicates the permissibility of using ploys and deception in the course of war with the disbelievers so as to cause harm to the enemies and brings benefits for the Muslims. This is not disliked in Islam; rather, it is recommended and desirable. Ibn al-Munayyir (may Allah have mercy upon him) said: "A war that is good and which achieves its intended objective is the war based on deception, not confrontation, for the former achieves victory without risk, while the latter involves danger." Treachery and violation of covenants, however, do not fall under deception. Allah, the Almighty, says: (If you [have reason to] fear from a people betrayal, throw [their treaty] back to them, [putting you] on equal terms. Indeed, Allah does not like traitors) [Sūrat al-Anfāl: 58]. That is notify them of the cancellation of the treaty before going to war against them, so that both of you will be on an equal footing.