Is Thinking About A Na-Mehram Also A Sin?
No, merely thinking about a person does not become a sin unless one makes a move towards adultery or commits adultery. ‘Zina‘ is prohibited in Islam and is a major sin. Acts which lead to Zina also known as precursors to Zina are minor sins like lustful gaze, physical touch and getting intimate etc. If someone has committed a minor sin like this but managed to control himself from major sin of Zina, then such minor sins will be forgiven in accordance with Quran: إِن تَجْتَنِبُواْ كَبَآئِرَ مَا تُنْهَوْنَ عَنْهُ نُكَفِّرْ عَنكُمْ سَيِّئَاتِكُمْ وَنُدْخِلْكُم مُّدْخَلاً كَرِيمًا If you abstain from the major sins of what is being prohibited to you, We shall forgive your minor sins and shall make you enter a place of honour . (Quran 4:31) The same has been stated by Prophet Muhammad (sws) in the following narration : https://sunnah.com/abudawud:2152 The above narration can be seen in the same context where person was able to refrain himself from a major sin after committing a minor sin. Please also refer to the video below from 4:49 onward https://youtu.be/l16ad6WN0Q0?t=289