Sahih Muslim 2994
Sahih Muslim · Book 55: The Book of Zuhd and Softening of Hearts · Saying: "May Allah Have Mercy On You" To One Who Sneezes, And Yawning Is Disliked
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
حَدَّثَنَا يَحْيَى بْنُ أَيُّوبَ ، وَقُتَيْبَةُ بْنُ سَعِيدٍ ، وَعَلِيُّ بْنُ حُجْرٍ السَّعْدِيُّ ، قَالُوا حَدَّثَنَا إِسْمَاعِيلُ، - يَعْنُونَ ابْنَ جَعْفَرٍ - عَنِ الْعَلاَءِ ، عَنْ أَبِيهِ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " التَّثَاؤُبُ مِنَ الشَّيْطَانِ فَإِذَا تَثَاءَبَ أَحَدُكُمْ فَلْيَكْظِمْ مَا اسْتَطَاعَ " .
The yawning as from the devil. So when one of you yawns he should try to restrain it as far as it lies in his power.