There are two kinds of Mujaahidah.
1. Physical Mujaahidah. This is the imposition of practices upon the nafs in order to accustom it to difficulties, e.g. accustoming the nafs to Salaat by imposing upon it Nafl Salaat in abundance; reducing the greed of the nafs by means of abundance of Nafl Fasting.
2. Opposition. In this type of Mujaahidah the nafs is opposed in its desires. When the nafs urges to commit sin then opposition is offered. The main type of mujaahidah is this second kind. This second kind of Mujaahidah is Waajib (compulsory). The first type of Mujaahidah is employed in order to acquire the second kind. When the nafs becomes accustomed to difficulties then it will develop the habit of controlling its desires.
Those who possess the ability to control their desires without resorting to physical Mujaahidah (the first kind) are not in need of this type of Mujaahidah. However, because such people are extremely few, the Sufiya have stringently adopted physical Mujaahidah as well. According to the Sufiya physical Mujaahidah consists of four fundamentals (Arkaan) as follows:
1. Qillat-e-Ta'aam: To eat less.
2. Qillat-e-Kalaam: To speak less.
3. Qillat-e-Manaam: To sleep less.
4. Qillat-e-Ikhtilaat Ma'al Anaam: To associate less with people.
One who fully acquires these four qualities and becomes accustomed to observe them, will attain the ability to control his nafs. He will be in a strong position to check the evil desires of the nafs.
Mujaahidah against the Nafs in its urges for sin is acquired when the nafs is opposed to a certain degree in even its lawful desires, e.g. refusal to fulfill immediately the desire of the nafs for some delicious food, its urge for such food being rebutted and only fulfilled after vehement desire so that the nafs does not become frustrated.
When one becomes accustomed to oppose the nafs in things lawful then it will become relatively simple to oppose the sinful urges of the nafs. A person who grants his nafs absolute freedom in the Mubaahaat (lawful things) at times will not be able to suppress the urge for sinning.