Imam Malik's Muwatta, Chapter: Shortening the Prayer

Yahya related to me from Malik that he had heard that Abdullah ibn Abbas used to shorten the prayer when he travelled a distance equivalent to that between Makka and Ta'if, and that between Makka and Usfan and that between Makka and Jedda. Malik said, "That is four mail-stages, and to me that is the most preferable distance for shortening the prayer." Malik said, "Someone who intends to travel does not shorten the prayer until he has left the houses of the village. And he does not do it in full until he comes to the first houses of the village, or is nearby."