“Maghdasi Shafi’i” quotes from “Ibn Sirin”:

و عن محمد بن سيرين: قيل له المهدي خير أو بكر وعمر رضى الله عنهما. قال هو خير منهما ويعدل بنبي.

“Ibn Sirin” was asked if Hadrat “Mahdi” [A.S] is better or “Abu-Bakr” and “Umar”? He said: “Mahdi” [A.S] is better than them {but} he’s the same as a Prophet.

Researcher of the book restates in footnote that the document of this narrative is authentic.

Aqd al-Durar fi Akhbar al-Muntazar – p 222