Yahya related to me from Malik from Nafi from Salim ibn Abdullahthat Abdullah ibn Umar rode to Dhat an-Nusub and shortened the prayeron the journey.Malik said, "There are four mail-stagesbetween Dhat an-Nusub and Madina." (DE)
USC-MSA web (English) reference: Book 9, Hadith 13 (DE)
Arabic reference (DE): Book 9, Hadith 341 (DE)