Musannaf Ibn Abi Shaybah

Hazrat Ibn Sirin says that when the muezzin gives the call to prayer, he should face the Qiblah. He considered it undesirable for the muezzin to stand in the minaret and turn around. Hasan used to say that the muezzin will face the Qiblah. When he says "Hayya 'ala-s-Salah," he should turn, and when he says "Allahu Akbar," he should face the Qiblah.