How Intrusive Thoughts Take a Hold of Us—If We Let Them
Imām Ibn Al-Qayyim, may Allāh have mercy on him, said:
One of [the paths to rectitude] is to be on one’s guard regarding [one’s] thoughts and to keep them safe. Caution, every caution, must be taken against becoming lax about [one’s bad thoughts] and allowing oneself to entertain them.
Indeed, this is because the root of all corruption comes along this direction, since [bad thoughts] are the seeds that the devil and [one’s own] soul [plant] into the soil of the heart. Then, if the seeds of those thoughts are able to take root, the devil takes it upon himself to water [them] from time to time until they become desires; then he waters them until they become definite decisions. After that, he keeps at them until they [actually] bear fruit as actions.
And there’s no doubt that pushing back [these initial bad] thoughts is easier than holding back desires or definite decisions: a slave [of Allāh] finds himself incapable, or just like one who’s incapable, of holding back [thoughts] after they’ve turned into absolute resolve, while he himself [is to be blamed] for his having been lax, not having pushed [those thoughts] back when they were [still just] feeble ideas. It’s like someone who pays little or no thought to a spark from a fire that lands on dry firewood; then, after it’s spread and taken over, he’s unable to put it out.
Ṭarīq Al-Hijratain, p. 377. Dār ʿĀlam Al-Fawāʾid.