Mishkat al-Masabih 19 Jihad كتاب الجهاد 48

وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الشَّهِيدُ لَا يَجِدُ أَلَمَ الْقَتْلِ إِلَّا كَمَا يَجِدُ أَحَدُكُمْ أَلَمَ الْقَرْصَةِ» . رَوَاهُ التِّرْمِذِيُّ وَالنَّسَائِيُّ وَالدَّارِمِيُّ وَقَالَ التِّرْمِذِيُّ: هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ

He reported God’s Messenger as saying, “The martyr experiences no more pain in being killed than one of you experiences from a sting.” Tirmidhi, Nasa’i and Darimi transmitted it, Tirmidhi saying this is a hasan gharib tradition.