The Messenger of Allah ﷺ said, "When one of you yawns, let him cover his mouth, for Satan enters through it."
حدثنا أحمد بن يونس حدثنا زهير عن سهيل عن ابن
قال رسول الله ﷺ إذا تثاءب أحدكم فليمسك على فيه فإن الشيطان يدخل
Muslim narrated it in Zuhd, chapter on saying "yarhamukallah" to one who sneezes and the dislike of yawning, hadith no. 2995, from the hadith of Suhayl bin Abu Salih, through this same chain.