Jabir ibn `Abdullah (may Allah be pleased with him) narrated that the Prophet (peace be upon him) said: "War is a deception." (1)
Explanation of vocabularies (2)
(deception which means khad`ah) may pronounced in three different ways, but the most eloquent is (Khad`ah). Tha`lab and others said: Khad`ah was the utterance of the Prophet (peace be upon him). The second is: (Khud`ah). The third is: (Khuda`ah) as An-Nawawy said. Al Mundhiry reported a fourth utterance which is (Khada`ah). The origin of the word is to show the outward of something and hide its reality.
Lessons gained from the Hadith: (3)
1- Ibn Al Munir said: The meaning of “war is a deception” is: The real meaning of war is to deceive the opponent and do not face it because of the great danger of confrontation and winning easily and fast without the danger of confrontation.
2- Exhortation to take heed during war and permissibility of deceiving the disbeliever, moreover the one who does not do so will become a prey to the deception of the disbelievers.
3- An-Nawawy said: Scholars agreed on the permissibility of deceiving the disbelievers in war as much as a person can do except in one case: When there is a treaty or a covenant with them, in this case it is not permissible to deceive them.
Ibn Al `Araby said: Deception in war is by tactics and setting ambushes and suchlike.
4- The Hadith contains a reference to having consultations during war because the need to consultation is confirmed more than showing courage.
5- Al Waqidy mentioned that the first time the Prophet (peace be upon him) said this was in the battle of Al Khandaq (the Trench).
(1) Reported by Al Bukhari No. (3030) and Muslim No. (4637).
(2) The commentary of An-Nawawy on Muslim (4 / 27) and Fathul-Bary of Ibn Hajar (9/ 31).
(3) See: The previous two references.