Yahya related to me from Malik from Da'ud ibn al-Husayn that IbnYarbu al-Makhzumi said, "I heard Zayd ibn Thabit say, 'The middleprayer is the prayer of dhuhr.' "
App reference: Book 8, Hadith 28
USC-MSA web (English) reference: Book 8, Hadith 28
Arabic reference: Book 8, Hadith 317