Answered by Shaykh Yūsuf Badāt
If a man’s mother was rubbing medicine on his arm and he was very scared of ḥurmat al-musāhra (incest) taking place. He made sure to control himself but felt a feeling in his private part. He is not sure if there was slight erection or not. Is Ḥurmat Al-Muṣāharah established? What is the ḤHHanafī ruling?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allāh, Most Gracious, Most Merciful.
Jazāk Allāh Khayr/ Thank you for contacting Mathabah Institute.
Ḥurmat Al-Muṣāharah incest is not established in the described scenario since there is doubt regarding whether the touch was accompanied by sexual temptation and lust. – (See: Rad Al-Muḥtār, Vol 3, Page 33, Dār Al-Fikr, Al-Qawāid Al-Fiqhīyyah, Page 15, Dār Al-Tirmidhī)
Ḥurmat Al-Muṣāharah is incest which is based on confirmed sexual temptations and lustful advances. – (See: Al-Bināyah Sharḥ Al-Hidāyah, Vol 4, Page 45, Dār Al-Kutub Al-‘Ilmīyyah)
Only Allāh knows best.
 وَالْعِبْرَةُ لِلشَّهْوَةِ عِنْدَ الْمَسِّ وَالنَّظَرِ لَا بَعْدَهُمَا وَحَدُّهَا فِيهِمَا تَحَرُّكُ آلَتِهِ أَوْ زِيَادَتُهُ بِهِ يُفْتَى – كتاب الدر المختار وحاشية ابن عابدين ج٣ /ص ٣٣ دار الفكر
 اليقين لا يزول بالشك
 الرجعة والمصاهرة يعني أنهما يثبتان بالقبلة بالشهوة وكذا بالمس وإن لم ينزل – كتاب البناية شرح الهداية ج٤/ ص٤٥ دار الكتب العلمية