Abu Huraira reported God’s Messenger as saying, “Yawning during prayer comes from the devil, so when one of you yawns he must restrain it as much as possible.” Tirmidhi transmitted it. In another version by him and by Ibn Majah it says, “He should put his hand over his mouth.”
Hadith Referenceمشكوة المصابيح / كتاب الصلاة / 993
Hadith Gradingالألبانی:صَحِيحٌ | زبیر علی زئی:صحيح
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «صحيح، رواه الترمذي (370 وقال: حسن صحيح، 1746) و ابن ماجه (968) [و للحديث شواھد عند البخاري (6223) وغيره .]»