Muwatta Malik Book 9, Hadith 14
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."
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 from Ibn Umar that he used to travel to Khaybar and he would shorten the prayer.