Umar (may Allah be well-pleased with him) was told that: During the time of Jahiliya (pre-Islamic era), a man would be subjected to injustice, so he would supplicate against the one who oppressed him, and [his supplication] would be answered quickly, and we do not see this happening in [the time of] Islam?

So he said:

That was the settlement between them and between injustice, and your appointed time (for full recompense) will be the Hour, and the Hour will be more grievous and more bitter.


[1] Muhadaraat Al-Udabaa by Al-Raaghib al-Asgahaani

[2] Benefited from:

قيل لعمر رضي الله عنه: كان الرجل في الجاهلية يُظلم فيدعو على من ظَلمه فيُجاب عاجلا ولا نرى ذلك في الإسلام
فقال: كان هذا جزاء بينهم وبين الظلم وإنّ موعدكم الآن الساعة والساعة أدهى وأمرّ