Muwatta Malik, Book 9, Hadith 375 (In-Book)

Yahya related to me from Malik from Hisham ibn Urwa that his father used to pray in the desert without a sutra.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، أَنَّ أَبَاهُ، كَانَ يُصَلِّي فِي الصَّحْرَاءِ إِلَى غَيْرِ سُتْرَةٍ ‏.‏

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also referenced under: Book 9, Hadith 44 (USC-MSA)