One of the Companions of the Prophet (peace and blessings be upon him) relates: In the Zuhr prayer, the recitation of the Prophet (peace and blessings be upon him) could be recognised by the movement of his beard.
Ahmad recorded it, and its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2683