Hadith 1:

 مُحَمَّدُ بْنُ الْحَسَنِ الطَّاطَرِيُّ عَمَّنْ ذَكَرَهُ عَنْ عَلِيِّ بْنِ النُّعْمَانِ عَنْ سُوَيْدٍ الْقَلانِسِيِّ عَنْ بَشِيرٍ الدَّهَّانِ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) قَالَ قُلْتُ لَهُ إِنِّي رَأَيْتُ فِي الْمَنَامِ أَنِّي قُلْتُ لَكَ إِنَّ الْقِتَالَ مَعَ غَيْرِ الإمَامِ الْمَفْرُوضِ طَاعَتُهُ حَرَامٌ مِثْلَ الْمَيْتَةِ وَالدَّمِ وَلَحْمِ الْخِنْزِيرِ فَقُلْتَ لِي هُوَ كَذَلِكَ فَقَالَ أَبُو عَبْدِ اللهِ (عَلَيْهِ السَّلام) هُوَ كَذَلِكَ هُوَ كَذَلِكَ.

Narrated from Basheer al-Dahhan, I said to Abu Abd-Allah Imam Sadiq (عليه السلام) that,  

I saw a dream in which I said to You, "Fighting alongside one who is not an Imam whose obedience is obligatory, is unlawful (Haram) just like consuming dead animals, blood and pork for food, and You said to me (in my dream), "That is how it is." 

Imam Sadiq (عليه السلام) then said, "That is how it is. That is how it is."

[Source: al-Kafi, Vol. 5, Pg. 28]

Hadith 2:

From a sermon of Imam Ali (عليه السلام):

انْظُرُوا أَهْلَ بَيْتِ نَبِيِّكُمْ فَالْزَمُوا سَمْتَهُمْ(4)، وَاتَّبِعُوا أَثَرَهُمْ فَلَنْ يُخْرِجُوكُمْ مِنْ هُدىً، وَلَنْ يُعِيدُوكُمْ فِي رَدىً، فَإِنْ لَبَدُوا فَالْبُدُوا(5)، وَإِنْ نَهَضُوا فَانْهَضُوا، وَلاَ تَسْبِقُوهُمْ فَتَضِلُّوا، وَلاَ تَتَأَخَّرُوا عَنْهُمْ فَتَهْلِكُوا

"Look at the AhlulBayt of your Prophet. Adhere to their path/direction. Follow their footsteps because they would never let you out of guidance, and never throw you into destruction. If they sit down, you sit down, and if they rise, then you rise. Do not go ahead of them, as you would thereby go astray and do not lag-behind them for you would perish."

[Source: Nahjul Balagha – Sermon 97]

Hadith 3:

From a sermon of Imam Ali (عليه السلام):

الْزَمُوا الاَرْضَ(2)، وَاصْبِروُا عَلَى الْبَلاءِ، وَلاَ تُحرِّكُوا بأَيْدِيكُمْ وَسُيُوفِكُمْ [فِي ]هَوَى أَلْسِنَتِكُمْ، وَلاَ تَسْتَعْجِلُوا بِمَا لَمْ يُعَجِّلْهُ اللهُ لَكُمْ، فَإِنّهُ مَنْ مَاتَ مِنْكُمْ عَلَى فِرَاشِهِ وَهُوَ عَلَى مَعْرِفَةِ حَقِّ رَبِّهِ عَزَّوَجَلّ وَحَقِّ رَسُولِهِ وَأَهْلِ بَيْتِهِ صَلَوَاتُ اللهِ عَلَيْهِ وَعَلَيْهِمْ مَاتَ شَهِيداً، وَوَقَعَ أَجْرُهُ عَلَى اللهِ، واسْتَوْجَبَ ثَوَابَ مَا نَوَى مِنْ صَالِحِ عَمَلِهِ، وَقَامَتِ النِّيَّةُ مَقَامَ إِصْلاَتِهِ لِسَيْفِهِ(3)، فإِنَّ لِكُلِّ شَيْء مُدَّةً وَأَجَلاً

"Stick to the earth, and be patient in trials, do not move/instigate your hands and your swords based on the desires of your tongues, and do not make haste in matters in which Allah has not hastened for you, because any one of you who dies in his bed having recognition (Marefat) of the rights of Allah and the rights of His Prophet (صلى الله عليه وآله) and the Prophets AhlulBayt (عليهم السلام), dies as a martyr (shaheed) and his reward is upon Allah. He is also deserving the recompense of the good acts he had intended to do, and his intention is counted as his drawing his sword. Certainly, for everything there is a time and a term."

[Source: Nahjul Balagha – Sermon 190]