Assalaamu alaykum. My question is the following: I thought about my fiancée that she could be like my mother a few hours after a light argument that her and I had on the phone. Is this thihaar? Is it still permissible for me to marry her? I did not say it out loud neither took an oath, but I do remember clearly thinking it in my head, or perhaps I whispered it to myself that she could be like my mother when thinking about the argument I had a few hours earlier. These ridiculous thoughts came to my mind; that she acts like my mother, and also that she is not that much younger than me, so how would I be able to marry her or even go close to her/get intimate with her once married. This thought particularly came to mind because of my fiancée’s age, as she is in her mid 30’s and I am in my late 30’s i.e. I was hoping for a younger woman. To give you context, I got engaged to this woman even though I did not find her attractive, but after doing istikhaarah (prayer of consultation) and looking at her other qualities, I decided to go ahead. I regret that it (thihaar) was an ill thought on my part and I should not have thought about it. Please advise whether all this constitutes thihaar or not and whether it is still permissible for me to go ahead with this marriage as no one knows about this i.e. what I thought, except for Allaah The Exalted?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

Firstly, you should know that the Muslim shall not be held accountable for the thoughts that cross his mind (as long as he does not talk about or act upon them). Abu Hurayrah narrated that the Prophet said, "Verily, Allaah forgave my ummah (community) the evil thoughts arising in their minds as long as they neither pronounced them nor acted upon them." [Al-Bukhari and Muslim]

Hence, you should pay no attention to inner thoughts that cross your mind as long you do not put them into words (or actions).

If you did actually utter the phrase mentioned in the question, then this does not count as explicit thihaar (i.e. the husband saying to his wife, "You are like my mother to me", i.e. "You are unlawful to me exactly like my mother"). Based on the context provided in the question, it seems that you meant that she was like her (your mother) in terms of age and the like. If this was the case, then this is not considered thihaar. Ibn Qudaamah wrote, "If a husband said to his wife, 'You are like my mother,' while intending to issue a thihaar, then it counts as one. However, if he intends it to be a mere expression of respect and appreciation or to indicate that she is like his mother in terms of old age or traits, then that does not count as thihaar. The criterion in this regard is the husband's intention..." [Al-Mughni]

Hence, there is no religious impediment to marrying this woman.

The age difference between the spouses does not constitute a valid religious impediment to their marriage according to the sharee'ah as well as common practice. If this woman is religious and well-mannered, then it is advisable that you marry her. If, on the other hand, you fear that your negative feelings about the age difference will hinder the continuity of your marriage, then it is better for you to reconsider marrying her. Canceling the engagement is less serious than terminating a marriage by divorce. It is allowable to cancel an engagement because it is a mere promise of marriage; however, it is disliked to cancel the engagement for no valid reason.

Allaah knows best.