Translation
(96) Holding Fast to the Qur'an and Sunnah
كتاب الاعتصام بالكتاب والسنة
(14) Chapter: “Certainly you will follow the ways of those who were before you.”
(14) باب قَوْلِ النَّبِيِّ صلى الله عليه وسلم ‏"‏ لَتَتْبَعُنَّ سَنَنَ مَنْ كَانَ قَبْلَكُمْ ‏"‏
Sahih al-Bukhari 7320 

Narrated Abu Sa`id Al-Khudri:

The Prophet (ﷺ) said, "You will follow the ways of those nations who were before you, span by span and cubit by cubit (i.e., inch by inch) so much so that even if they entered a hole of a mastigure, you would follow them." We said, "O Allah's Messenger (ﷺ)! (Do you mean) the Jews and the Christians?" He said, "Whom else?"

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الْعَزِيزِ، حَدَّثَنَا أَبُو عُمَرَ الصَّنْعَانِيُّ ـ مِنَ الْيَمَنِ ـ عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ عَطَاءِ بْنِ يَسَارٍ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ لَتَتْبَعُنَّ سَنَنَ مَنْ كَانَ قَبْلَكُمْ شِبْرًا شِبْرًا وَذِرَاعًا بِذِرَاعٍ، حَتَّى لَوْ دَخَلُوا جُحْرَ ضَبٍّ تَبِعْتُمُوهُمْ ‏"‏‏.‏ قُلْنَا يَا رَسُولَ اللَّهِ الْيَهُودُ وَالنَّصَارَى قَالَ ‏"‏ فَمَنْ ‏"‏‏.‏
Reference : Sahih al-Bukhari 7320
In-book reference : Book 96, Hadith 50
USC-MSA web (English) reference : Vol. 9, Book 92, Hadith 422
  (deprecated numbering scheme)