Struggle against the self is the greater jihad
Widely repeated despite a weak chain of transmission, this saying gave Sufi ethical writers, al-Ghazali included, a durable vocabulary for treating the struggle against one's own appetites and pride as combat, not passive self-improvement.
The saying reports the Prophet returning from a military campaign and telling his companions, "We have returned from the lesser jihad to the greater jihad," identifying that greater struggle as the fight against one's own nafs. Sufi ethical writers, al-Ghazali among them across the Ihya, cite it constantly to reframe jihad primarily as an interior discipline, resisting appetite, anger, pride, and heedlessness, rather than only armed struggle, and to justify treating self-mastery with the same seriousness classical Islam gave to warfare. It is worth knowing that hadith specialists widely consider the chain of transmission for this saying weak or its wording apocryphal, so its authority in Sufi literature rests on centuries of use and coherence with Qur'anic material on self-struggle rather than on a strong isnad. Whatever its precise origin, it gave later writers a durable vocabulary for describing inner effort as combat rather than passive improvement.
We have returned from the lesser jihad to the greater jihad.
Hadith specialists generally classify this saying as weak or without a reliable chain of transmission, despite its wide currency in Sufi ethical literature.