Sahih Muslim 2995 b
The son of Abu Said al-Khudri reported on the authority of his father that Allah's Messenger (ﷺ) said:
When one of you yawns, he should try to restrain it with cue help of his hand since it is the Satan that enters therein.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، عَنْ سُهَيْلٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي،
 سَعِيدٍ عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ إِذَا تَثَاوَبَ أَحَدُكُمْ فَلْيُمْسِكْ بِيَدِهِ
 فَإِنَّ الشَّيْطَانَ يَدْخُلُ ‏"‏ ‏.‏