What is the ruling on sexual fantasies and thoughts that come to a person involuntarily regarding a female friend of his?

It is not permissible to conjure up sexual fantasies and derive pleasure from them. However, if such thoughts overwhelm a person without being intentionally summoned, there is no blame. Nevertheless, one should strive to repel them and not indulge in them, as they are the root of corruption. Ibn al-Qayyim said: "Guarding thoughts, preserving them, and being wary of neglecting them or indulging in them, for the root of all corruption comes from them."

The relationship between the sexes has শরীয়াহ-based regulations, and leniency in observing them leads to severe consequences. Mixing [between sexes] in studies is a gateway to temptation. Those who are compelled to study should observe the শরীয়াহ-based regulations, such as lowering the gaze, avoiding seclusion, and refraining from unnecessary speech.