Muwatta Imam Malik Book of Shortening the Prayer, Hadith 13

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."

حَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، رَكِبَ إِلَى ذَاتِ النُّصُبِ فَقَصَرَ الصَّلاَةَ فِي مَسِيرِهِ ذَلِكَ . قَالَ مَالِكٌ وَبَيْنَ ذَاتِ النُّصُبِ وَالْمَدِينَةِ أَرْبَعَةُ بُرُدٍ .