Sahih Muslim 155 f
It is narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) observed:
What would you do when the son of Mary would descend amongst you and would lead you as one amongst you? Ibn Abi Dhi'b on the authority of Abu Huraira narrated: Your leader amongst you. Ibn Abi Dhi'b said: Do you know what the words:" He would lead as one amongst you" mean? I said: Explain these to me. He said: He would lead you according to the Book of your: Lord (hallowed be He and most exalted) and the Sunnah of your Apostle (ﷺ).
وَحَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنِي الْوَلِيدُ بْنُ مُسْلِمٍ، حَدَّثَنَا ابْنُ أَبِي ذِئْبٍ، عَنِ ابْنِ شِهَابٍ، عَنْ نَافِعٍ، مَوْلَى أَبِي قَتَادَةَ عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ كَيْفَ أَنْتُمْ إِذَا نَزَلَ فِيكُمُ ابْنُ مَرْيَمَ فَأَمَّكُمْ مِنْكُمْ ‏"‏ ‏.‏ فَقُلْتُ لاِبْنِ أَبِي ذِئْبٍ إِنَّ الأَوْزَاعِيَّ حَدَّثَنَا عَنِ الزُّهْرِيِّ عَنْ نَافِعٍ عَنْ أَبِي هُرَيْرَةَ ‏"‏ وَإِمَامُكُمْ مِنْكُمْ ‏"‏ ‏.‏ قَالَ ابْنُ أَبِي ذِئْبٍ تَدْرِي مَا أَمَّكُمْ مِنْكُمْ قُلْتُ تُخْبِرُنِي ‏.‏ قَالَ فَأَمَّكُمْ بِكِتَابِ رَبِّكُمْ تَبَارَكَ وَتَعَالَى وَسُنَّةِ نَبِيِّكُمْ صلى الله عليه وسلم ‏.‏