Yahya related to me from Malik from Ibn Shihab from Salim ibnAbdullah that his father rode to Rim and shortened the prayer on thejourney.Malik said, "That was about four mail-stages."(approximately forty-eight miles). (ES)
USC-MSA web (English) reference: Book 9, Hadith 12 (ES)
Arabic reference (ES): Book 9, Hadith 340 (ES)