Al-Kāfi - Volume 5 > Kinds of Jihad (struggle)
Hadith #3

3- عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ النَّوْفَلِيِّ عَنِ السَّكُونِيِّ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) أَنَّ النَّبِيَّ (صَلَّى اللهُ عَلَيْهِ وَآلِه) بَعَثَ بِسَرِيَّةٍ فَلَمَّا رَجَعُوا قَالَ مَرْحَباً بِقَوْمٍ قَضَوُا الْجِهَادَ الأصْغَرَ وَبَقِيَ الْجِهَادُ الأكْبَرُ قِيلَ يَا رَسُولَ اللهِ (صَلَّى اللهُ عَلَيْهِ وَآلِه) وَمَا الْجِهَادُ الأكْبَرُ قَالَ جِهَادُ النَّفْسِ.

3. Ali ibn Ibrahim has narrated from his father from al-Nawfaliy from al-Sakuniy who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that the Messenger of Allah once mobilized a group of people against the enemy. When they returned back he said, ’I welcome a people who have just come back after completion of the minor Jihad and who yet have to complete the major Jihad.’ Someone then asked, ‘What is the major Jihad, O Messenger of Allah?’ He replied, ‘It is Jihad against the desires of one’s own soul to disobey Allah.’”