Musnad Abu Ya'la al-Mawsili 129:145

And from Anas, that a man asked the Prophet, peace and blessings of Allah be upon him, about the time of the dawn prayer. So he commanded Bilal, and he gave the call to prayer for the dawn prayer, then he performed the iqamah, and he prayed. When it was the next day, he delayed until it became bright. Then he commanded him, and he performed the iqamah, and he prayed. When he finished, he said, "Where is the questioner?" The man stood up and said, "Here I am." He said, "Between these two is the time."