Hadith 2:43
He also reported among the material he knew to come from God’s messenger that he said, "At the beginning of every century God will send one who will renew its religion for this people.” Abu Dawud transmitted it.
وَعَنْهُ فِيمَا أَعْلَمُ عَنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّ اللَّهَ عَزَّ وَجَلَّ يَبْعَثُ لِهَذِهِ الْأُمَّةِ عَلَى رَأْسِ كُلِّ مِائَةٍ سَنَةٍ مَنْ يُجَدِّدُ لَهَا دِينَهَا» . رَوَاهُ أَبُو دَاوُد
Original Reference: Mishkat al-Masabih 247