Jami` at-Tirmidhi 2165
Ibn 'Umar narrated:
" 'Umar delivered a Khutbah to us at Al-Jabiyah. He said: 'O you people! Indeed I have stood among you as the Messenger of Allah(s.a.w) stood among us, and he said: "I order you (to stick to) my Companions, then those who come after them, then those who come after them. Then lying will spread until a man will take an oath when no oath was sought from him, and a witness will testify when his testimony was not sought. Behold! A man is not alone with a woman but the third of them is Ash-Shaitan. Adhere to the Jama'ah, beware of separation, for indeed Ash-Shaitan is with one, and he is further away from two. Whoever wants the best place in Paradise, then let him stick to the Jama'ah. Whoever rejoices with his good deeds and grieves over his evil deeds, then that is the  believer among you.'"
حَدَّثَنَا أَحْمَدُ بْنُ مَنِيعٍ، حَدَّثَنَا النَّضْرُ بْنُ إِسْمَاعِيلَ أَبُو الْمُغِيرَةِ، عَنْ مُحَمَّدِ بْنِ سُوقَةَ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، قَالَ خَطَبَنَا عُمَرُ بِالْجَابِيَةِ فَقَالَ يَا أَيُّهَا النَّاسُ إِنِّي قُمْتُ فِيكُمْ كَمَقَامِ رَسُولِ اللَّهِ صلى الله عليه وسلم فِينَا فَقَالَ ‏
"‏ أُوصِيكُمْ بِأَصْحَابِي ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ يَفْشُو الْكَذِبُ حَتَّى يَحْلِفَ الرَّجُلُ وَلاَ يُسْتَحْلَفُ وَيَشْهَدَ الشَّاهِدُ وَلاَ يُسْتَشْهَدُ أَلاَ لاَ يَخْلُوَنَّ رَجُلٌ بِامْرَأَةٍ إِلاَّ كَانَ ثَالِثَهُمَا الشَّيْطَانُ عَلَيْكُمْ بِالْجَمَاعَةِ وَإِيَّاكُمْ وَالْفُرْقَةَ فَإِنَّ الشَّيْطَانَ مَعَ الْوَاحِدِ وَهُوَ مِنَ الاِثْنَيْنِ أَبْعَدُ مَنْ أَرَادَ بُحْبُوحَةَ الْجَنَّةِ فَلْيَلْزَمِ الْجَمَاعَةَ مَنْ سَرَّتْهُ حَسَنَتُهُ وَسَاءَتْهُ سَيِّئَتُهُ فَذَلِكَ الْمُؤْمِنُ ‏"‏ ‏.‏ قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ مِنْ هَذَا الْوَجْهِ وَقَدْ رَوَاهُ ابْنُ الْمُبَارَكِ عَنْ مُحَمَّدِ بْنِ سُوقَةَ وَقَدْ رُوِيَ هَذَا الْحَدِيثُ مِنْ غَيْرِ وَجْهٍ عَنْ عُمَرَ عَنِ النَّبِيِّ صلى الله عليه وسلم ‏.‏