When you sneeze , then say : Alḥamdulillāh Your companion should say : Yarḥamukallāh When someone says Yarḥamukallāh to you then you should say: Yahdīkumu ‘llāhu wa yuṣliḥu bālakum. 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. Reference: Al-Bukhari 7/125.

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