Hadith
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، أَنَّ أَبَاهُ، كَانَ يُصَلِّي فِي الصَّحْرَاءِ إِلَى غَيْرِ سُتْرَةٍ .
Yahya related to me from Malik from Hisham ibn Urwa that his father used to pray in the desert without a sutra
Sahih · Salim al-Hilali
Muwatta Malik 372 ·Book 9, Hadith 47·Also available on sunnah.com·