“No one in this world other than Abu Ahmad al-Zubayri attributed it directly to the Prophet.” Al-Hakim said: “Its chain of transmission is authentic.” Al-Dhahabi concurred.

From the legal understanding of the hadith:

Ibn Khuzaymah said: “This report indicates that an obligatory prayer may not be performed before its time begins.” He further said: “The phrase ‘a dawn at which food becomes prohibited’ refers to the fasting person, and ‘prayer becomes permissible’ refers to the morning prayer. The phrase ‘a dawn at which prayer becomes prohibited’ refers to the morning prayer: when the first dawn appears, it is not permissible to perform the morning prayer at that time, because the first dawn occurs during the night. He did not mean that it is impermissible to offer voluntary prayers after the first dawn. And the phrase ‘food becomes permissible’ refers to one who intends to fast.”