COVER YOUR MOUTH WHEN YOU YAWN H 897 "When you yawn you should cover your mouth with your hand or else satan will enter." R 897 Muslim with a chain up to Abu Sa'id Khudri who related that the Prophet, praise and peace be upon him, said this.
884- وعن أَبي سعيد الخدري رضي الله عنه ، قَالَ : قَالَ رسول الله صلى الله عليه وآله وسلم : "إِذَا تَثَاءبَ أحَدُكُمْ فَلْيُمْسِكْ بِيَدِهِ عَلَى فِيهِ ؛ فَإنَّ الشَّيْطَانَ يَدْخُلُ" رواه مسلم .