Yahya related to me from Malik from Zayd ibn Aslam that Ata ibnYasar said, "A man came to the Messenger of Allah, may Allah bless himand grant him peace, and asked him about the time of the subh prayer.The Messenger of Allah, may Allah bless him and grant him peace, didnot answer him, but in the morning he prayed subh at first light. Thefollowing morning he prayed subh when it was much lighter, and thensaid, 'Where is the man who was asking about the time of the prayer?'The man replied, 'Here I am, Messenger of Allah.' He said,'The time isbetween these two.' "
Arabic/English book reference: Book 1, Hadith 3