Reference : Hisn al-Muslim 188

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 :
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.

Chapter: Upon sneezing