Bayhaqi 1769 — The end of the preferred time for the Fajr prayer

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that a man asked about the time of the Subh prayer, so he (peace and blessings be upon him) ordered Bilal (may Allah be pleased with him), and he gave the adhan when the dawn broke; then he called the iqamah and he (peace and blessings be upon him) led the prayer. When the next morning came, he (peace and blessings be upon him) delayed it until it became bright; then he (peace and blessings be upon him) ordered him to call the iqamah, so he called the iqamah and he (peace and blessings be upon him) led the prayer. Then he (peace and blessings be upon him) called the man and said: "Were you present at the prayer today and yesterday?" He said: Yes. He (peace and blessings be upon him) said: "Between this and this is the time (of the prayer)."
Its meaning has also been narrated in the hadith of Buraydah bin al-Husayb from the Prophet (peace and blessings be upon him), and it is a sahih (authentic) hadith.