The Prophet ﷺ said, "Yawning during prayer is from Satan, so when one of you yawns, let him suppress it as much as he can."
حدثنا علي بن حجر أخبرنا إسمعيل بن جعفر عن العلاء بن عبد الرحمن عن أبيه
أن النبي ﷺ قال التثاؤب في الصلاة من الشيطان فإذا تثاءب أحدكم فليكظم ما استطاع
GradingMuslim also narrated it in Zuhd, chapter on responding to the sneezer and the disapproval of yawning, hadith no. 2994, from Ali bin Hajar, through the same route. There is another route for it in Bukhari, hadith no. 6226, from Abu Hurairah, through the same route. On this subject there is also a narration from Abu Saeed Khudri [Muslim, no. 2995] and from the grandfather of Adi bin Thabit [to come, no. 2748].