[Machine] The Prophet ﷺ said, "A man should not be alone with a woman, and a woman should not travel unless she is accompanied by a mahram."  

النَّبِيَّ ﷺ يَقُولُ لَا يَخْلُوَنَّ رَجُلٌ بِامْرَأَةٍ وَلَا تُسَافِرُ امْرَأَةٌ إِلَّا وَمَعَهَا ذُو مَحْرَمٍ  

Messenger of Allah ﷺ said, "Beware of entering upon the ladies." A man from the Ansar said, "Allah's Apostle! What about Al-Hamu the in-laws of the wife (the brothers of her husband or his nephews etc.)?" The Prophet ﷺ replied: The in-laws of the wife are death itself. (Using translation from Bukhārī 5232)   

أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِيَّاكُمْ وَالدُّخُولَ عَلَى النِّسَاءِ فَقَالَ رَجُلٌ مِنَ الْأَنْصَارِ أَرَأَيْتَ الْحَمْوَ قَالَ الْحَمْوُ الْمَوْتُ  

I did not see but good only (in my wife). Thereupon Messenger of Allah ﷺ said: Verily Allah has made her immune from all this. Then Messenger of Allah ﷺ stood on the pulpit and said: After this day no man should enter the house of another person in his absence, but only when he is accompanied by one person or two persons. (Using translation from Muslim 2173)   

أَنَّ نَفَرًا مِنْ بَنِي هَاشِمٍ دَخَلُوا عَلَى أَسْمَاءَ بِنْتِ عُمَيْسٍ فَدَخَلَ أَبُو بَكْرٍ الصِّدِّيقُ ؓ وَهِيَ تَحْتَهُ يَوْمَئِذٍ فَرَآهُمْ فَكَرِهَ ذَلِكَ وَذَكَرَ ذَلِكَ لِرَسُولِ اللهِ ﷺ وَقَالَ لَمْ أَرَ إِلَّا خَيْرًا فَقَالَ رَسُولُ اللهِ ﷺ إِنَّ اللهَ ﷻ قَدْ بَرَّأَهَا مِنْ ذَلِكَ ثُمَّ قَامَ رَسُولُ اللهِ ﷺ عَلَى الْمِنْبَرِ فَقَالَ لَا يَدْخُلَنَّ رَجُلٌ بَعْدَ يَوْمِي هَذَا عَلَى مُغِيبَةٍ إِلَّا وَمَعَهُ رَجُلٌ أَوِ اثْنَانِ لَفْظُ حَدِيثِ الْمُقْرِئِ  

[Machine] That he sent him to Ali, seeking his permission to see Asma bint Umayyad, so he granted him permission. After he finished his business, he asked the owner, Umar, about it, so he said, "Indeed, the Messenger of Allah ﷺ prohibited us from entering upon women without the permission of their husbands."  

أَنَّهُ أَرْسَلَهُ إِلَى عَلِيٍّ ؓ يَسْتَأْذِنُهُ عَلَى أَسْمَاءَ بِنْتِ عُمَيْسٍ فَأَذِنَ لَهُ حَتَّى إِذَا فَرَغَ مِنْ حَاجَتِهِ سَأَلَ الْمَوْلَى عَمْرًا عَنْ ذَلِكَ فَقَالَ إِنَّ رَسُولَ اللهِ ﷺ نَهَانَا أَوْ نَهَى أَنْ نَدْخُلَ عَلَى النِّسَاءِ بِغَيْرِ إِذْنِ أَزْوَاجِهِنَّ  

The Messenger of Allah ﷺ stood before us as I am standing before you, and said: ʿI urge you to show respect to my Companions, then those who come after them, then those who come after them, then lying will become so widespread that a man will start to give testimony before he is asked to do so.Whoever among you wants to attain a spacious abode in Paradise, let him adhere to the jama'ah (main body of Muslims), for the Shaitan is with the one who is alone, but he is further away from two. And no one of you should be alone with a woman for the Shaitan will be the third one present. The one who is pleased with his good deeds and upset by his bad deeds is a believer.ʿ (Using translation from Aḥmad 114)   

فَقَامَ فِينَا رَسُولُ اللهِ ﷺ مَقَامِي فِيكُمْ فَقَالَ اسْتَوْصُوا بِأَصْحَابِي خَيْرًا ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ يَفْشُو الْكَذِبُ حَتَّى إِنَّ الرَّجُلَ لَيَبْتَدِئُ بِالشَّهَادَةِ قَبْلَ أَنْ يُسْأَلَهَا وَبِالْيَمِينِ قَبْلَ أَنْ يُسْأَلَهَا فَمَنْ أَرَادَ مِنْكُمْ بَحْبَحَةَ الْجَنَّةِ فَلْيَلْزَمِ الْجَمَاعَةَ فَإِنَّ الشَّيْطَانَ مَعَ الْوَاحِدِ وَهُوَ مِنَ الِاثْنَيْنِ أَبْعَدُ وَلَا يَخْلُوَنَّ أَحَدُكُمْ بِامْرَأَةٍ فَإِنَّ الشَّيْطَانَ ثَالِثُهُمَا وَمَنْ سَرَّتْهُ حَسَنَتُهُ وَسَاءَتْهُ سَيِّئَتُهُ فَهُوَ مُؤْمِنٌ وَاللهُ سُبْحَانَهُ وَتَعَالَى أَعْلَمُ