What does this hadith mean, what does it mean by no barrier. The Prophet Said: "Fear the dua (supplication) of the oppressed, for indeed there is no barrier between it and Allah." (Bukhari)

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

This Hadeeth shows the seriousness of injustice, and it is a warning against injustice. It also highlights that the supplication of the wronged person against his oppressor is answered, and that there is nothing that would prevent it [his supplication] from being answered. Rather, the supplication of a wronged person is heard and it is not rejected.

Al-Mubaarakfoori said in Tuhfat Al-Ahwathi: (Guard against the supplication of the oppressed), meaning, avoid injustice, for fear that the oppressed person will supplicate against you (as there is no veil between it and Allaah) there is nothing to prevent it from reaching Allaah; rather, it is presented to Him. As-Suyooti said: i.e. there is nothing that will prevent it, even if the oppressed himself has something that requires that his supplication is not answered, like if his food is ill-gotten and the like. Even, some narrations of the Hadeeth read: (...even if he [the wronged person] is a disbeliever).” [End of quote]

For more information, please refer to Fatwa 130288.

Allaah Knows best.