When someone yawns, he should put his hand overhis mouth Al-Adab Al-Mufrad 950
Arabic hadith text
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.
Translation
Ibn Abbas said, "When someone yawns, he should place his hand over his mouth. Yawning comes from Shaytan."