ENOfficial
He reported God’s messenger as saying, “He who copies any people is one of them.” Ahmad and Abu Dawud transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ تَشَبَّهَ بِقَوْمٍ فَهُوَ مِنْهُمْ» . رَوَاهُ أَحْمد وَأَبُو دَاوُد
sunnah.com