Hadithcore
Mishkat al-Masabih, 4347

He reported God’s messenger as saying, “He who copies any people is one of them.” Ahmad and Abu Dawud transmitted it.

وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ تَشَبَّهَ بِقَوْمٍ فَهُوَ مِنْهُمْ» . رَوَاهُ أَحْمد وَأَبُو دَاوُد

References1 variant
In-Book Reference
Book 22, Hadith 39