قال الشيخ رحمه الله ومن ظن انه على طهارة فصلى ثم علم بعد ذلك انه على غير طهارة تطهر وأعاد الصلاة وكذلك من صلى في ثوب وظن انه طاهر ثم عرف بعد ذلك انه كان نجسا ففرط في صلاته فيه من غير تأمل له أعاد الصلاة فقد بينا ذلك في باب الطهارة وشرحناه ويؤكده ايضا ما رواه
So the meaning of this narration is that if one does not turn entirely behind but only turns slightly to the right or to the left, then this does not invalidate the prayer, even though it detracts from it. As for when the turning is complete, then it does invalidate the prayer, as we have previously explained. The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: ‘Whoever assumes that he is in a state of purity and prays, then later realizes that he was not in a state of purity, he must perform purification and repeat the prayer. Likewise, whoever prays in a garment thinking it is pure, and then finds out afterward that it was impure, and he was negligent in checking it beforehand, must repeat the prayer.’ We have already explained and clarified this in the chapter on purification, and it is also confirmed by what was narrated:
