77. Upon sneezing

إِذَا عَطَسَ أَحَدُكُم فَلْيَقُلِ (الْحَمْدُ لِلَّهِ)، وَلْيَقُلْ لَهُ أَخُوهُ أَوْ صَاحِبُهُ: (يَرْحَمُكَ اللَّهُ)، فَإِذَا قَالَ لَهُ: (يَرحَمُكَ اللَّهُ)، فَلْيَقُلْ: (يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُمْ)

When you sneeze, then say: All praises and thanks are to Allah. Your companion should say: May Allah have mercy upon you. When someone says Yarḥamukallāh to you then you should say: May Allah guide you and set your affairs in order.

Source: Al-Bukhari 7/125.