جَاءَ رَجُلٌ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ دُلَّنِي عَلَى عَمَلٍ يَعْدِلُ الْجِهَادَ. قَالَ " لاَ أَجِدُهُ ـ قَالَ ـ هَلْ تَسْتَطِيعُ إِذَا خَرَجَ الْمُجَاهِدُ أَنْ تَدْخُلَ مَسْجِدَكَ فَتَقُومَ وَلاَ تَفْتُرَ وَتَصُومَ وَلاَ تُفْطِرَ ". قَالَ وَمَنْ يَسْتَطِيعُ ذَلِكَ قَالَ أَبُو هُرَيْرَةَ إِنَّ فَرَسَ الْمُجَاهِدِ لَيَسْتَنُّ فِي طِوَلِهِ فَيُكْتَبُ لَهُ حَسَنَاتٍ.
Bukhari: A man came to God's Apostle and said, "Instruct me as to such a deed as equals Jihad in reward". He replied, "I do not find such a deed. Can you, while the Muslim fighter has gone out for Jihad, enter a mosque to perform prayers without ceasing and fast forever?" The man said, "No one can do that." (Volume 4, Book 52, Number 44)
Many narrations used by enemies of Islam are similar to the one presented above. All these narrations emphasize the importance of Jihad in Islam. The purpose of Jihad is emphasized clearly in the Qur'an:
4:75 And what is wrong with you that you fight not in the Cause of Allah, and for those weak, ill-treated and oppressed among men, women, and children, whose cry is: "Our Lord! Rescue us from this town whose people are oppressors; and raise for us from You one who will protect, and raise for us from You one who will help
We can understand the Jihad the Prophet Muhammad (peace be upon him) encouraged if we examine the historical situation at that time. Muhammad Husayn Haykal notes the following in his biography of the Prophet Muhammad (peace be upon him):
Fighting was permitted in Islam, and carried out by Muhammad and his companions, in order to stop their being persecuted for their faith and to have all the freedom they needed to call men to it. Later, when we see the details and the proofs of this, it will become clear that in all these alliances Muhammad's purpose was the consolidation of the defence of Madinah. The objective was to remove Madinah beyond any design the Quraysh might have against its Muslim inhabitants. Muhammad could not have forgotten that the Makkans once sought to extradite the Muslims from Abyssinia... ...This peaceful show of strength by Islam does not at all mean that Islam, at that time, forbade fighting in defence of personal life and of religion, or to put a stop to persecution. Indeed, Islam did not. Rather, it imposed such defence as a sacred duty. What it did really mean at that time, as it does today or will ever do, was to condemn any war of aggression. "Do not commit any aggression," God commands. He counsels, "God does not love the aggressors."[Qur'an, 2:190] (Haykal, The Life of Muhammad; US North American Trust Publications, 1976, p.206, 208 emphasis added)
Therefore, Islam, being a system which aims for the betterment of humanity, imposes fighting against oppression and injustice as a religious duty. This is the reason for the sayings of the Prophet Muhammad (peace be upon him) which encourage his followers to fight for the sake of God.