Anas ibn Malik reported: The Messenger of Allah, peace and blessings be upon him, said, “Beware of the supplication of the oppressed, even if he is an unbeliever, for there is no screen between it and Allah.”
I’m not 100% sure of the interpretation of this Hadith, but I think it means the following–
Allah s.w.t. is always with the oppressed. He listens to their prayers, and is most receptive to the oppressed (person’s) prayers, in particular.
So, if you have oppressed someone (in any way, great or “small”), and that person prays to Allah (to, for example, bring justice to the situation)…. you should fear (because justice might be brought upon you, the oppressor).
(What this Hadith is really getting at is that you shouldn’t oppress anyone, for, it may be that if/when the person whom you have oppressed prays to Allah (while there is ‘no screen’ between he and Allah) for help, Allah will apportion the justice (and you as the oppressor in that situation will bear the grunt of it).
This is so even in the case of a non-Muslim (i.e., a non-Muslim praying to Allah for help against oppression done to him… even by a Muslim!)
How just (and great) is our religion-! Because it is governed by none other than the Sovereign, Himself. (s.w.t.)
Ya Allah, let us oppress no one in our lives, in any way, and if we do, help us fix the situation. a..and please make us just and compassionate people. ameen.