Authentic
graded by Al-Albani
Mishkat al-Masabih 3118
Narrator:Umar ibn al-Khattāb
وَعَنْ عُمَرَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَا يَخْلُوَنَّ رَجُلٌ بِامْرَأَةٍ إِلَّا كَانَ ثالثهما الشَّيْطَان» . رَوَاهُ التِّرْمِذِيّ
‘Umar reported the Prophet as saying, "Whenever a man is alone with a woman the devil makes a third.” Tirmidhi transmitted it.
Cited in Mishkat al-Masabih (No. 3118).