Muwatta Malik, Book 41, Hadith 17 (USC-MSA)

Malik related to me from Abu'z-Zinad that he said, ''Umar ibn Abd al-Aziz flogged a slave with eighty lashes for slander." Abu'z-Zinad said, "I asked Abdullah ibn Amir ibn Rabia about that. He said, 'I saw Umar ibn al-Khattab, Uthman ibn Affan, the Khalifs, and so on, and I did not see any of them flog a slave more than forty lashes for slander.' "

حَدَّثَنِي مَالِكٌ، عَنْ أَبِي الزِّنَادِ، أَنَّهُ قَالَ جَلَدَ عُمَرُ بْنُ عَبْدِ الْعَزِيزِ عَبْدًا فِي فِرْيَةٍ ثَمَانِينَ ‏.‏ قَالَ أَبُو الزِّنَادِ فَسَأَلْتُ عَبْدَ اللَّهِ بْنَ عَامِرِ بْنِ رَبِيعَةَ عَنْ ذَلِكَ فَقَالَ أَدْرَكْتُ عُمَرَ بْنَ الْخَطَّابِ وَعُثْمَانَ بْنَ عَفَّانَ وَالْخُلَفَاءَ هَلُمَّ جَرًّا فَمَا رَأَيْتُ أَحَدًا جَلَدَ عَبْدًا فِي فِرْيَةٍ أَكْثَرَ مِنْ أَرْبَعِينَ ‏.‏

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also referenced under: Book 41, Hadith 1519 (In-Book)