Sahih al-Bukhari, Book 96, Hadith 39 (In-Book) ⓘ

Narrated Al-A`mash: I asked Abu Wail, "Did you witness the battle of Siffin between `Ali and Muawiya?" He said, "Yes," and added, "Then I heard Sahl bin Hunaif saying, 'O people! Blame your personal opinions in your religion. No doubt, I remember myself on the day of Abi Jandal; if I had the power to refuse the order of Allah's Messenger, I would have refused it. We have never put our swords on our shoulders to get involved in a situation that might have been horrible for us, but those swords brought us to victory and peace, except this present situation.' " Abu Wail said, "I witnessed the battle of Siffin, and how nasty Siffin was!"

حَدَّثَنَا عَبْدَانُ، أَخْبَرَنَا أَبُو حَمْزَةَ، سَمِعْتُ الأَعْمَشَ، قَالَ سَأَلْتُ أَبَا وَائِلٍ هَلْ شَهِدْتَ صِفِّينَ قَالَ نَعَمْ‏.‏ فَسَمِعْتُ سَهْلَ بْنَ حُنَيْفٍ، يَقُولُ ح وَحَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنِ الأَعْمَشِ، عَنْ أَبِي وَائِلٍ، قَالَ قَالَ سَهْلُ بْنُ حُنَيْفٍ يَا أَيُّهَا النَّاسُ اتَّهِمُوا رَأْيَكُمْ عَلَى دِينِكُمْ، لَقَدْ رَأَيْتُنِي يَوْمَ أَبِي جَنْدَلٍ وَلَوْ أَسْتَطِيعُ أَنَّ أَرُدَّ أَمْرَ رَسُولِ اللَّهِ صلى الله عليه وسلم لَرَدَدْتُهُ، وَمَا وَضَعْنَا سُيُوفَنَا عَلَى عَوَاتِقِنَا إِلَى أَمْرٍ يُفْظِعُنَا إِلاَّ أَسْهَلْنَ بِنَا إِلَى أَمْرٍ نَعْرِفُهُ غَيْرَ هَذَا الأَمْرِ‏.‏ قَالَ وَقَالَ أَبُو وَائِلٍ شَهِدْتُ صِفِّينَ وَبِئْسَتْ صِفُّونَ‏.‏