Hadith 3118
Mishkat al-Masabih
Marriage · Looking at a Woman who is asked in Marriage, and an Explanation of what may not be seen - Section 2
Arabic
وَعَنْ عُمَرَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَا يَخْلُوَنَّ رَجُلٌ بِامْرَأَةٍ إِلَّا كَانَ ثالثهما الشَّيْطَان» . رَوَاهُ التِّرْمِذِيّ
English translation
‘Umar reported the Prophet (ﷺ) as saying, "Whenever a man is alone with a woman the devil makes a third.” Tirmidhi transmitted it.