Musannaf Ibn Abi Shayba 3:5748

Hushaym narrated to us, he said: Al-Mughirah informed us, from Ibrahim, who said: Al-Harith said to him, "Do you shorten the prayer to Al-Mada'in?" He said, "Al-Mada'in is near, but [shorten it] to Al-Ahwaz and what is similar to it."