Beware of the supplication of the oppressed

The Prophet, may the peace and blessings of Allah be upon him, warned his companions severely against committing injustice, and its grave painful consequences. On the other hand he called them to support the oppressed by all the legitimate means, encouraged them to take care of freedoms and to maintain the honor and property of others so that they establish justice among people in all cases. The Prophet may the peace and blessings of Allah be upon him, informed that the doors of the Heavens is open to the supplication of the oppressed , therefore it will not ever be rejected, because Allah has forbidden injustice to Himself and He has made it forbidden among people. In other words evil consequences of injustice will befall the one who commits injustice. 
The meaning of the words of the Prophet, may the peace and blessings of Allah be upon him, in this commandment is: " for there is no barrier between it and Allah." 
Is that it is unconditionally responded to and is raised directly to Allah for judgment. Once the oppressed supplicate to Allah whereas he is assured that Allah will respond to him, he will have his supplication answered.