SHAFAQNA – Ayah 78 of Surah Al-Isra says: “Perform Salaat at the decline of the sun (from its meridian) until the darkness of the night and (also) the Quran of dawn. Indeed the recitation of the dawn is ever witnessed.” The “Quran of dawn” (Fajr Salaat or Morning Prayer) is witnessed by the angels of the day and the angels of the night. In the above holy verse, the “Quran” means something that is recited and it refers to the Fajr Salaat .
The above holy verse says: The Fajr Salaat is witnessed; the question which comes to mind is who are the witnesses? According to the narrations: The Fajr Salaat is witnessed by the angels of the night and the angels of the day because at the start of the morning the night angels are replaced by the day angels and as the Fajr Salaat starts right at the beginning of the day, both groups of angels are witnesses to the Fajr Salaat .
 Tafseer Nemoneh, Footnote for Ayah 78 of Surah Al-Isra.
 Alkafi, (Al-Islamiyah), Vol. 8, Page 341.