Good Manners and Form (Al-Adab)
Ṣaḥīḥ al-Bukhārī 6223
إِنَّ اللَّهَ يُحِبُّ الْعُطَاسَ، وَيَكْرَهُ التَّثَاؤُبَ، فَإِذَا عَطَسَ فَحَمِدَ اللَّهَ، فَحَقٌّ عَلَى كُلِّ مُسْلِمٍ سَمِعَهُ أَنْ يُشَمِّتَهُ، وَأَمَّا التَّثَاوُبُ فَإِنَّمَا هُوَ مِنَ الشَّيْطَانِ، فَلْيَرُدَّهُ مَا اسْتَطَاعَ، فَإِذَا قَالَ هَا. ضَحِكَ مِنْهُ الشَّيْطَانُ
inna-Llāh yuḥibbu al-ʿuṭāsa, wayakrah at-tathāʾuba, fa-idhā ʿaṭasa faḥamida-Llāh, faḥaqqun ʿalā kulli muslimin samiʿah an yushammitah, wa-ammā at-tathāwubu fa-innamā huwa mina ash-shayṭāni, falyaruddah mā āstaṭāʿa, fa-idhā qāla hā. ḍaḥika minhu ash-shayṭānu
Transliteration generated from the Arabic vowel marks
The full narration
Narrated Abu Huraira:The Prophet (ﷺ) said, "Allah likes sneezing and dislikes yawning, so if someone sneezes and then praises Allah, then it is obligatory on every Muslim who heard him, to say: May Allah be merciful to you (Yar-hamuka-l-lah). But as regards yawning, it is from Satan, so one must try one's best to stop it, if one says 'Ha' when yawning, Satan will laugh at him
Source
Ṣaḥīḥ al-Bukhārī · 6223