Yahya related to me from Malik that he had heard that Urwa ibnaz-Zubayr and Said ibn al-Musayyab used to pray voluntary prayerssitting. (AR)
App reference (AR): Book 8, Hadith 25 (AR)
USC-MSA web (English) reference: Book 8, Hadith 25 (AR)
Arabic reference (AR): Book 8, Hadith 314 (AR)