Muwatta Imam Malik Book of Prayer in Congregation, Hadith 16

Yahya related to me from Malik from Yahya ibn Said that a man used to lead the people in prayer in al-Aqiq (a place near Madina), and Umar ibn Abd al-Aziz sent a message to him forbidding him to do so.
Malik said, "He only forbade him because his father was not known."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّ رَجُلاً، كَانَ يَؤُمُّ النَّاسَ بِالْعَقِيقِ فَأَرْسَلَ إِلَيْهِ عُمَرُ بْنُ عَبْدِ الْعَزِيزِ فَنَهَاهُ . قَالَ مَالِكٌ وَإِنَّمَا نَهَاهُ لأَنَّهُ كَانَ لاَ يُعْرَفُ أَبُوهُ .