حَدَّثَنِي أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، عَنْ سُفْيَانَ، عَنْ سُهَيْلِ بْنِ أَبِي صَالِحٍ، عَنِ ابْنِ أَبِي سَعِيدٍ الْخُدْرِيِّ، عَنْ أَبِيهِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا تَثَاوَبَ أَحَدُكُمْ فِي الصَّلاَةِ فَلْيَكْظِمْ مَا اسْتَطَاعَ فَإِنَّ الشَّيْطَانَ يَدْخُلُ " .
The son of Abu Said al-Khudri reported on the authority of his father that Allah's Messenger (PBUH) said. When one of you yawns while engaged in prayer, he should try to restrain so far as it lies in his power, since it is the Satan that enter therein. Translation Not Available
Book Ref: Sahih Muslim Book 55 Hadith 7132
Web Ref: Sahih Muslim Book 42 Hadith 2995 c