When someone yawns, he should put his hand overhis mouth

Al-Adab Al-Mufrad · Book 40 · Hadith 949

حَدَّثَنَا مُسَدَّدٌ، قَالَ‏:‏ حَدَّثَنَا خَالِدٌ، قَالَ‏:‏ حَدَّثَنَا سُهَيْلٌ، عَنِ ابْنِ أَبِي سَعِيدٍ، عَنْ أَبِي سَعِيدٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ‏:‏ إِذَا تَثَاءَبَ أَحَدُكُمْ فَلْيَضَعْ يَدَهُ بِفِيهِ، فَإِنَّ الشَّيْطَانَ يَدْخُلُ فِيهِ‏.‏

Abu Sa'id reported that the Prophet, may Allah bless him and grant him peace, said, "When one of you yawns, he should put his hand over his mouth. Otherwise Shaytan might enter it."

Al-Adab Al-Mufrad · Book 40 · Hadith 950

حَدَّثَنَا عُثْمَانُ، قَالَ‏:‏ حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ هِلاَلِ بْنِ يَسَافٍ، عَنْ عَطَاءٍ، عَنِ ابْنِ عَبَّاسٍ قَالَ‏:‏ إِذَا تَثَاءَبَ فَلْيَضَعْ يَدَهُ عَلَى فِيهِ، فَإِنَّمَا هُوَ مِنَ الشَّيْطَانِ‏.‏

Ibn Abbas said, "When someone yawns, he should place his hand over his mouth. Yawning comes from Shaytan."