Imam Al-Nawawi's Riyad-us-Saliheen
Chapter 48
Warning against persecution of the Pious, the Weak and the Indigent

Allah, the Exalted, says:

"And those who annoy believing men and women undeservedly, they bear (on themselves) the crime of slander and plain sin.'' (33:58)

"Therefore, treat not the orphan with oppression. And repulse not the beggar.'' (93:9,10)

389. Jundub bin Abdullah (May Allah be pleased with him) reported: Messenger of Allah (sallallaahu ’alayhi wa sallam) said, "He who performs the Fajr (dawn) prayer comes under the Protection of Allah, so beware lest Allah questions you about what you owe Him. For if He questions anyone of you and he falls short of fulfilling the duty which he owes Him, He will requite and then throw upon his face into the Hell-fire".
[Muslim].

Commentary:  A Muslim who performs Fajr prayer receives the protection of Allah. But he who does not fall short of fulfilling the duty which he to owes Allah. It also serves a warning in case of not observing such duty, Allah will demand failing to it. If He does, Hell will be the requital. This highlights the merit of performing the Fajr prayer with congregation, while the second warns a Muslim that since he has started that day by a pledge with Allah, he must keep it for the full day and abstain from doing anything which goes against it.