The people of the Book used to let their hair hand down, and the polytheists used to part their hair. The Messenger of Allah ﷺ like to confirm with the People of the Book in the matters about which he had received no command. Hence he Messenger of Allah ﷺ let his forelock hang down but afterwards he parted it. (Using translation from Abū Dāʾūd 4188)
كَانَ الْمُشْرِكُونَ يَفْرُقُونَ رُءُوسَهُمْ وَكَانَ أَهْلُ الْكِتَابِ يَسْدِلُونَ قَالَ يَعْقُوبُ أَشْعَارَهُمْ وَكَانَ رَسُولُ اللهِ ﷺ يُحِبُّ وَيُعْجِبُهُ مُوَافَقَةُ أَهْلِ الْكِتَابِ قَالَ يَعْقُوبُ فِي بَعْضِ مَا لَمْ يُؤْمَرْ قَالَ إِسْحَاقُ فِيمَا لَمْ يُؤْمَرْ فِيهِ فَسَدَلَ نَاصِيَتَهُ ثُمَّ فَرَقَ بَعْدُ