Abu Salih reported that the Prophet, may Allah bless him and grant him peace, said, "When one of you sneezes, he should say, 'Praise be to Allah.' When he says, 'Praise be to Allah, ' his brother or companion should say to him, 'May Allah have mercy on you.' Then let the person who sneezed say, 'May Allah guide you and put your affairs in order.'"  

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا عَطَسَ أَحَدُكُمْ فَلْيَقُلِ الْحَمْدُ لِلَّهِ فَإِذَا قَالَ الْحَمْدُ لِلَّهِ فَلْيَقُلْ لَهُ أَخُوهُ أَوْ صَاحِبُهُ يَرْحَمُكَ اللَّهُ وَلْيَقُلْ هُوَ يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُمْ  

Abu Hurayra reported that the Prophet, may Allah bless him and grant him peace, said, "Allah loves the sneeze and dislikes yawning. When one you sneezes and praises Allah, it is a duty for every Muslim who hears him to say, 'May Allah have mercy on you.;' As for the yawn, it comes from Shaytan. When one of you yawns, he should repress it as much as possible. When one of you yawns, Shaytan laughs at him."  

عَنِ النَّبِيِّ ﷺ قَالَ إِنَّ اللَّهَ يُحِبُّ الْعُطَاسَ وَيَكْرَهُ التَّثَاؤُبَ وَإِذَا عَطَسَ أَحَدُكُمْ وَحَمِدَ اللَّهَ كَانَ حَقًّا عَلَى كُلِّ مُسْلِمٍ سَمِعَهُ أَنْ يَقُولَ يَرْحَمُكَ اللَّهُ فَأَمَّا التَّثَاؤُبُ فَإِنَّمَا هُوَ مِنَ الشَّيْطَانِ فَإِذَا تَثَاءَبَ أَحَدُكُمْ فَلْيَرُدَّهُ مَا اسْتَطَاعَ فَإِنَّ أَحَدَكُمْ إِذَا تَثَاءَبَ ضَحِكَ مِنْهُ الشَّيْطَانُ  

Ibn 'Abbas said, "When someone is wished mercy, he should say, 'May Allah protect us and you from the Fire. May Allah have mercy on you.'"  

سَمِعْتُ ابْنَ عَبَّاسٍ يَقُولُ إِذَا شُمِّتَ عَافَانَا اللَّهُ وَإِيَّاكُمْ مِنَ النَّارِ يَرْحَمُكُمُ اللَّهُ  

Abu Hurayra said, "We were sitting with the Messenger of Allah, may Allah bless him and grant him peace, when a man sneezed and praised Allah. The Messenger of Allah, may Allah bless him and grant him peace, said to him, 'May Allah have mercy on you.' Then another man sneezed but the Prophet did not say anything to him. The man, 'Messenger of Allah! you responded to the other man, but did not say anything to me!' The Prophet replied, 'He praised Allah and you were silent.'"  

عَنْ أَبِي هُرَيْرَةَ قَالَ كُنَّا جُلُوسًا عِنْدَ رَسُولِ اللهِ ﷺ فَعَطَسَ رَجُلٌ فَحَمِدَ اللَّهَ فَقَالَ لَهُ رَسُولُ اللهِ ﷺ يَرْحَمُكَ اللَّهُ ثُمَّ عَطَسَ آخَرُ فَلَمْ يَقُلْ لَهُ شَيْئًا فَقَالَ يَا رَسُولَ اللهِ رَدَدْتَ عَلَى الْآخَرِ وَلَمْ تَقُلْ لِي شَيْئًا؟ قَالَ إِنَّهُ حَمِدَ اللَّهَ وَسَكَتَّ