Hadith on Mahdi: Earth to be filled with justice by the Mahdi

Abu Sa’id al-Khudri reported: The Messenger of Allah, peace and blessings be upon him, said, “The Mahdi will be from my lineage, with a curved nose. He will fill the earth with justice and equity, just as it had been filled with tyranny and oppression. He will rule for seven years.

Source: Sunan Abī Dāwūd 4285

Grade: Sahih (authentic) according to Al-Suyuti

عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ الْمَهْدِيُّ مِنِّي أَجْلَى الْجَبْهَةِ أَقْنَى الْأَنْفِ يَمْلَأُ الْأَرْضَ قِسْطًا وَعَدْلًا كَمَا مُلِئَتْ جَوْرًا وَظُلْمًا يَمْلِكُ سَبْعَ سِنِينَ

4285 سنن أبي داود كتاب المهدي

9225 المحدث السيوطي خلاصة حكم المحدث صحيح في الجامع الصغير