حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ حَدَّثَنَا يُونُسُ عَنِ الزُّهْرِيِّ عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ عَنِ ابْنِ عَبَّاسٍ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَسْدِلُ شَعَرَهُ وَكَانَ الْمُشْرِكُونَ يَفْرُقُونَ رُءُوسَهُمْ وَكَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُحِبُّ مُوَافَقَةَ أَهْلِ الْكِتَابِ فِيمَا لَمْ يَنْزِلْ عَلَيْهِ فَفَرَقَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ رَأْسَهُ
مسند امام احمد بن حنبل · Hadith 2944
It was narrated from Ibn 'Abbas (RA) that the Prophet (PBUH) used to let his hair hang down (over his forehead), and the mushrikoon used to part their hair. The People of the Book used to let their hair hang down over their foreheads and the Prophet (PBUH) liked to do the same as the People of the Book in matters concerning which he had not received any revelation. Then (later on) the Messenger of Allah (PBUH) parted his hair.
Sanad
حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ حَدَّثَنَا يُونُسُ عَنِ الزُّهْرِيِّ عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ عَنِ ابْنِ عَبَّاسٍ