Sunan Ibn Majah Book 21, Hadith 2658

حَدَّثَنَا عَلْقَمَةُ بْنُ عَمْرٍو الدَّارِمِيُّ، حَدَّثَنَا أَبُو بَكْرِ بْنُ عَيَّاشٍ، عَنْ مُطَرِّفٍ، عَنِ الشَّعْبِيِّ، عَنْ أَبِي جُحَيْفَةَ، قَالَ قُلْتُ لِعَلِيِّ بْنِ أَبِي طَالِبٍ هَلْ عِنْدَكُمْ شَىْءٌ مِنَ الْعِلْمِ لَيْسَ عِنْدَ النَّاسِ قَالَ لاَ وَاللَّهِ مَا عِنْدَنَا إِلاَّ مَا عِنْدَ النَّاسِ إِلاَّ أَنْ يَرْزُقَ اللَّهُ رَجُلاً فَهْمًا فِي الْقُرْآنِ أَوْ مَا فِي هَذِهِ الصَّحِيفَةِ فِيهَا الدِّيَاتُ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَنْ لاَ يُقْتَلَ مُسْلِمٌ بِكَافِرٍ ‏.‏

It was narrated that Abu Juhaifah said:“I said to 'Ali bin Abu Talib: 'Do you have any knowledge that the people do not have?' He said: 'No, by Allah, we only know what the people know, except that Allah may bless a man with understanding of Qur'an or what is in this sheet, in which are mentioned the rulings on blood money from the Messenger of Allah (ﷺ) and it says that a Muslim should not be killed in retaliation for the murder of disbeliever.'”