From Sahih Bukhari (Hadith 746):
Narrated Abu Ma`mar:We asked Khabbab whether Allah's Messenger (ﷺ) used to recite (the Qur'an) in the Zuhr and the `Asr prayers. He replied in the affirmative. We said, "How did you come to know about it?" He said, "By the movement of his beard
Reference: Bukhari 746