Is it haram for an unmarried girl to imagine sexual relationships and foreplay between a man and a woman, and what is the textual and rational proof for that, and what is the difference between this and what occurs between spouses?

Fleeting thoughts and imaginations do not entail sin as long as they remain as such. However, indulging in them is blameworthy because it exposes the soul to satanic provocations and incites the commission of prohibitions, and it may turn into an addiction. A Muslim woman should occupy her time with what benefits her in her religion and her worldly life. The imagination of repulsive images is not comparable to the imagination of sexual intercourse between spouses, for marriage permits enjoyment and looking at the 'awrah (private parts), let alone imagining intercourse.