Maliks Muwatta Book 9, Hadith Number 8.

Section : Shortening the Prayer in Travel.

Yahya related to me from Malik from Ibn Shihab from a man of the family of Khalid ibn Asid that he said to Abdullah ibn Umar, “Abu Abd ar-Rahman, we find the fear prayer and the prayer when settled mentioned in the Qur’an, but we do not find any mention of the travelling prayer in it.” Ibn Umar said, “Son of my brother! Allah the Mighty and Majestic sent us Muhammad, may Allah bless him and grant him peace, and we know nothing. We only do as we saw him doing.”