Fortress of the Muslim (Hisn al-Muslim)
حصن المسلم
(77) Chapter: Upon sneezing
(77) دعاء العطاس
Hisn al-Muslim 188 
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)

Reference : Hisn al-Muslim 188