(97) باب مَا جَاءَ فِي التَّثَاؤُبِ
Abu Sa'id al-Khudri reported the Messenger of Allah (May peace be upon him) as saying:
When one of you yawns, he should hold his hand over his mouth, for the devil enters.
Reference: Sunan Abi Dawud 5026
In-book reference: Book 43, Hadith 254
English translation: Book 42, Hadith 5008