Abu Hurayrah, Allah be pleased with him narrates that the Prophet, Allah send peace and blessings upon him said, ”When one of you sneezes he should say,

All praise is due to Allah

and his brother or companion (who heard him say Alhamdulillah upon sneezing) should say

Allah have mercy on you

When he says ‘Yarhamuk Allah’ then he should reply by saying

Allah guide you and rectify your affairs

عَنْ أَبِي هُرَيْرَةَ ، رَضِيَ اللَّهُ عَنْهُ ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ : إِذَا عَطَسَ أَحَدُكُمْ فَلْيَقُلِ

الْحَمْدُ لِلَّهِ

وَلْيَقُلْ لَهُ أَخُوهُ ، أَوْ صَاحِبُهُ

يَرْحَمُكَ اللَّهُ

فَإِذَا قَالَ لَهُ يَرْحَمُكَ اللَّهُ فَلْيَقُلْ

يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُمْ

(رواه البخاري، باب إذا عطس كيف يشمّت)