وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، عَنْ أَبِيهِ، أَنَّهُ رَكِبَ إِلَى رِيمٍ فَقَصَرَ الصَّلاَةَ فِي مَسِيرِهِ ذَلِكَ ‏.‏ قَالَ مَالِكٌ وَذَلِكَ نَحْوٌ مِنْ أَرْبَعَةِ بُرُدٍ ‏.‏

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). Translation Not Available

Book Ref: Muwatta Imam Malik Book 9 Hadith 340
Web Ref:  Muwatta Imam Malik Book 9 Hadith 12