Sahih Bukhari Volume 5, Book 64, Hadith 4191

حَدَّثَنَا الْحَسَنُ بْنُ إِسْحَاقَ، حَدَّثَنَا مُحَمَّدُ بْنُ سَابِقٍ، حَدَّثَنَا مَالِكُ بْنُ مِغْوَلٍ، قَالَ سَمِعْتُ أَبَا حَصِينٍ، قَالَ قَالَ أَبُو وَائِلٍ لَمَّا قَدِمَ سَهْلُ بْنُ حُنَيْفٍ مِنْ صِفِّينَ أَتَيْنَاهُ نَسْتَخْبِرُهُ فَقَالَ اتَّهِمُوا الرَّأْىَ، فَلَقَدْ رَأَيْتُنِي يَوْمَ أَبِي جَنْدَلٍ وَلَوْ أَسْتَطِيعُ أَنْ أَرُدَّ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم أَمْرَهُ لَرَدَدْتُ، وَاللَّهُ وَرَسُولُهُ أَعْلَمُ، وَمَا وَضَعْنَا أَسْيَافَنَا عَلَى عَوَاتِقِنَا لأَمْرٍ يُفْظِعُنَا إِلاَّ أَسْهَلْنَ بِنَا إِلَى أَمْرٍ نَعْرِفُهُ قَبْلَ هَذَا الأَمْرِ، مَا نَسُدُّ مِنْهَا خُصْمًا إِلاَّ انْفَجَرَ عَلَيْنَا خُصْمٌ مَا نَدْرِي كَيْفَ نَأْتِي لَهُ

Narrated By Abu Wail : When Sahl bin Hunaif returned from (the battle of) Siffin, we went to ask him (as to why he had come back). He replied, "(You should not consider me a coward) but blame your opinions. I saw myself on the day of Abu Jandal (inclined to fight), and if I had the power of refusing the order of Allah's Apostle then, I would have refused it (and fought the infidels bravely). Allah and His Apostle know (what is convenient) better. Whenever we put our swords on our shoulders for any matter that terrified us, our swords led us to an easy agreeable solution before the present situation (of disagreement and dispute between the Muslims). When we mend the breach in one side, it opened in another, and we do not know what to do about it."