What is the ruling on thinking about the forms of the wide-eyed houris, and what might arouse lust, and what is the ruling on thinking about having intercourse with them?

A person is not held accountable for mere self-talk unless they act upon it or speak it. However, if thinking and imagining lead to falling into a forbidden act, such as masturbation, then it is not permissible.

Indulging in intrusive thoughts is a gateway to temptation and corruption. Satan may lure one into thinking about non-mahram women until he seduces them through these thoughts, and this may lead to committing indecency.

Ibn Al-Qayyim stated that the root of all corruption stems from neglecting intrusive thoughts and indulging in them, because they are the seeds sown by Satan and the self in the heart. If they take root, Satan tends to them by watering them until they become intentions, then firm resolves, and then bear the fruit of actions. Repelling intrusive thoughts is easier than repelling intentions and firm resolves. Whoever neglects to repel them when they are weak thoughts is like one who disregards a spark of fire in dry wood; when it takes hold, he becomes unable to extinguish it.

Among the ways to guard one's thoughts are: firm knowledge of Allah's awareness and observation of the heart and His knowledge of thoughts; modesty before Him; glorifying Him from seeing such thoughts in His abode; fearing to fall from His regard; preferring His love above all others; fearing the generation of these thoughts and the burning of faith; knowing that thoughts are like a snare for hunting a bird; recognizing that evil thoughts do not coexist with faith; understanding that they are a sea of imagination in which the heart drowns; and realizing that they are the valley of fools and the delusions of the ignorant.

The legitimate way to overcome lust is marriage for those who are able, or fasting while guarding one's hearing and sight for those who are not able, occupying oneself with what benefits in religion and worldly life, accompanying the righteous, and increasing supplication and seeking refuge in Allah.