عَنِ ابْنِ عَبَّاسٍ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُصُّ أَوْ يَأْخُذُ مِنْ شَارِبِهِ وَكَانَ إِبْرَاهِيمُ خَلِيلُ الرَّحْمَنِ صَلَوَاتُ الرَّحْمَنِ عَلَيْهِ يَفْعَله. رَوَاهُ التِّرْمِذِيّ
Translation

‘Amr b. Shu'aib; on his father's authority, said his grandfather told that the Prophet used to take something off the side and the bottom of his beard. Tirmidhi transmitted it, saying this is a gharib tradition.