Muwatta Malik Book 9, Hadith 13
Yahya related to me from Malik from Ibn Shihab from Salim ibn
Abdullah that his father rode to Rim and shortened the prayer on the
journey.
Malik said, "That was about four mail-stages."
(approximately forty-eight miles).
Yahya related to me from Malik from Nafi that Abdullah ibn Umar, shortened the prayer when he left for hajj or umra at Dhu'l Hulayfa.
Yahya related to me from Malik from Nafi from Salim ibn Abdullah that Abdullah ibn Umar rode to Dhat an-Nusub and shortened the prayer on the journey.
Malik said, "There are four mail-stages between Dhat an-Nusub and Madina."