[Jihād Against the Hypocrites]

Answer: The word jihād linguistically means to exert effort to the utmost — whether in advice, in battle, or in any action that concerns a person or benefits others.
Thus, one who exerts himself in seeking knowledge is called a mujāhid (striver); one who strives earnestly to advise the Muslims is called a mujāhid; and one who works diligently to maintain kindness toward his parents and ties of kinship is also called a mujāhid, and so on.
Therefore, the Prophet (May Allah bless him and his family and grant them peace) fulfilled Allah’s command in this verse by striving to his utmost in fighting the polytheists, and also by striving to the utmost in advising the hypocrites, countering their plots, nullifying their corruption, and warning against them. It is upon this understanding that the famous hadith came: “We have returned from the lesser jihād to the greater jihād,” meaning the struggle against one’s own self.
As for His saying, Exalted is He: “Not equal are those believers remaining [at home] – other than the disabled – and the mujahideen [who strive and fight] in the cause of Allah…” [An-Nisāʾ:95], the mujāhidīn here refers to those who fight with the sword and engage in combat, as indicated by their contrast with those who remain behind.
And His saying, Exalted is He: “And you strive in the cause of Allah with your wealth and your lives…” [As-Saff:11], also refers to fighting, as the context shows.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3