The Messenger of Allah (sal Allahu alaihi wa sallam) prayed: “O Allah, bless my Ummah (in their work) in the early part of the morning.” [Tirmidhi]
The time after the commencement of Fajr is a time of immense blessings (Barakah). To receive this Barakah we must be awake.
Sleeping after Fajr is a discouraged practice, unless one is ill, weak or has some other valid reason. If we need to sleep we should do so after sunrise, although it’s better to take a short nap in the afternoon.