Bukhari

� Lexical Explanation:
«اتَّقِ دَعْوَةَ الْمَظْلُوْمِ» Beware of the supplication of the oppressed, and the way to do this is not to wrong him so that he does not supplicate against you.
«لَيْسَ بَيْنَهَا وَبَيْنَ اللهِ حِجَابٌ» There is no veil between Allah and him, meaning Allah accepts his supplication immediately.
In one narration, it is stated that there is no doubt in the acceptance of the supplication of the oppressed. [حسن الصحيحة 596، صحيح ابوداود 1584، صحيح الادب المفرد 24]
In another narration, it is mentioned that the supplication of the oppressed rises towards the sky like burning embers. [صحيح : صحيح الترغيب 2228، صحيح الجامع الصغير 118]
According to another Prophetic statement, even if the oppressed is a disbeliever (kafir), one should still beware of his supplication. [حسن صحيح الجامع الصغير 119، سلسلة الصحيحة الباني:767]

Hadith Commentary:
(1)
The meaning of "no barrier intervening" is that the supplication (du'a) of the oppressed is accepted very swiftly. Thus, Imam Ibn Abi Shaybah rahimahullah has narrated from Abu Hurairah radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam said:
"The supplication of the oppressed is certainly accepted, even if he is a sinner (fajir).
He will bear the consequences of his own sinfulness, but his supplication will not be rejected."
(al-Musannaf li-Ibn Abi Shaybah: 10/96, and al-Sahihah of al-Albani, under hadith: 767)

(2)
Its meaning is not that the oppressor is immediately seized by Allah, rather Allah ta'ala deals with him as He wills.
Sometimes He punishes immediately, and sometimes He delays the reckoning so that the oppressor may commit further injustice, and ultimately He seizes him suddenly.
In any case, the oppressor should not think that he has committed oppression but has not received any punishment.
A respite may be granted by Allah, but injustice is not possible with Him.

Explanation:
1:
The meaning is that the supplication of the oppressed is accepted very swiftly;
therefore, always keep away from oppression and transgression,
otherwise, you will become the target of the sigh (curse) of the oppressed.