Abu Ma'mar (may Allah have mercy on him) said: We asked Sayyiduna Khabbab (may Allah be pleased with him): Did the Messenger of Allah (peace and blessings be upon him) recite (the Qur'an) in the Zuhr and Asr prayers? He said: Yes. We asked: How did you know? He said: "By the movement of his jaws."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3668