Musnad Ahmad 114
It was narrated from Ibn 'Umar that 'Umar bin al-Khattab addressed us in al-Jabiyah, and said:
The Messenger of Allah ﷺ  stood before us as I am standing before you, and said: `I 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.`
حَدَّثَنَا عَلِيُّ بْنُ إِسْحَاقَ، أَنْبَأَنَا عَبْدُ اللَّهِ يَعْنِي ابْنَ الْمُبَارَكِ، أَنْبَأَنَا مُحَمَّدُ بْنُ سُوقَةَ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، رَضِيَ اللَّهُ عَنْهُ خَطَبَ النَّاسَ بِالْجَابِيَةِ فَقَالَ قَامَ فِينَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مِثْلَ مَقَامِي فِيكُمْ فَقَالَ اسْتَوْصُوا بِأَصْحَابِي خَيْرًا ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ يَفْشُو الْكَذِبُ حَتَّى إِنَّ الرَّجُلَ لَيَبْتَدِئُ بِالشَّهَادَةِ قَبْلَ أَنْ يُسْأَلَهَا فَمَنْ أَرَادَ مِنْكُمْ بَحْبَحَةَ الْجَنَّةِ فَلْيَلْزَمْ الْجَمَاعَةَ فَإِنَّ الشَّيْطَانَ مَعَ الْوَاحِدِ وَهُوَ مِنْ الِاثْنَيْنِ أَبْعَدُ لَا يَخْلُوَنَّ أَحَدُكُمْ بِامْرَأَةٍ فَإِنَّ الشَّيْطَانَ ثَالِثُهُمَا وَمَنْ سَرَّتْهُ حَسَنَتُهُ وَسَاءَتْهُ سَيِّئَتُهُ فَهُوَ مُؤْمِنٌ‏.‏