It was narrated that Abu Ma’mar said:“I said to Khabbab: ‘How did you recognize that the Messenger of Allah (ﷺ) was reciting in the Zuhr and the ‘Asr?’ He said: ‘From the movement of his beard.’”
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا الأَعْمَشُ، عَنْ عُمَارَةَ بْنِ عُمَيْرٍ، عَنْ أَبِي مَعْمَرٍ، قَالَ قُلْتُ لِخَبَّابٍ بِأَىِّ شَىْءٍ كُنْتُمْ تَعْرِفُونَ قِرَاءَةَ رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ فِي الظُّهْرِ وَالْعَصْرِ قَالَ بِاضْطِرَابِ لِحْيَتِهِ .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 826