Hazrat Abu Hurairah (radhiyallahu ‘anhu) narrates that Rasulullah (sallallahu ‘alaihi wasallam) said:

إن الله يبعث لهذه الأمة على رأس كل مائة سنة من يجدد لها دينها (سنن أبي داود #4291)

Indeed Allah Ta‘ala sends for this Ummah, on the expiry of every one hundred years, a person who will revive their Deen for them.

Imaam Ahmed bin Hambal (rahimahullah) has mentioned the following:

Indeed Allah Ta‘ala sends for the Ummah, at the termination of every century, a personality who will teach them (and revive) the Sunnah, and purify the Deen of Rasulullah (sallallahu ‘alaihi wasallam) from fabrications and unfounded practices. When we reflected (over personalities who fitted this description), we had found that Hazrat ‘Umar bin ‘Abdul ‘Azeez (rahimahullah) was the personality who was blessed to revive Deen at the termination of the first century, and Imaam Shaafi‘ee (rahimahullah) was the personality who was blessed to revive Deen at the termination of the second century.”

(Siyar A’laam min Nubalaa 10/46)