Chapter on the Detailed Explanation of Prayer, Including the Obligatory and Recommended, and What is Permissible and Not Permissible.

And from him, from Ahmad ibn Idris from Ahmad ibn Muhammad, and Muhammad ibn Yahya from Muhammad ibn Ahmad ibn Yahya from Ahmad ibn al-Hasan ibn Ali from ‘Amr ibn Sa’id from Musaddiq ibn Sadaqah from ‘Ammar al-Sabati: Abu Abdillah عليه السلام (was asked) regarding a man who prays not facing the Qiblah and then realizes while he is still in the prayer before finishing it. Imam عليه السلام said: "If he is facing a direction between the east and the west, then let him turn his face toward the Qiblah as soon as he realizes. But if he is facing the rear of the Qiblah, then he must break the prayer, turn his face toward the Qiblah, and then begin the prayer anew."