Mishkat al-Masabih 22 Clothing كتاب اللباس 128

وَعَنْ عَمْرِو بْنِ شُعَيْبٍ عَنْ أَبِيهِ عَنْ جَدِّهِ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَأْخُذُ مِنْ لِحْيَتِهِ مِنْ عَرْضِهَا وَطُولِهَا. رَوَاهُ التِّرْمِذِيُّ وَقَالَ: هَذَا حَدِيثٌ غَرِيبٌ

‘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.