Muwatta Malik Book 9, Hadith 12
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 Yahya ibn Said that he said to Salim ibn Abdullah, "What is the latest you have seen your father delay maghrib while on a journey?" and Salim replied, "One time the sun set when we were at Dhat al-Jaysh and he prayed maghrib at al- Aqiq."
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).