Sahih Bukhari
Sahih Bukhari Volume 001, Book 012, Hadith Number 727.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 12. Charecteristics Of Prayer
Narated By Abu Ma'mar : I asked Khabbab whether the Prophet 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 that?" He said, "From the movement of his beard."