1. The Prophet (pbuh) said :When one of you sneezes he should say,

Alhamdhulillah

اَلْحَمْدُ للهِ

Meaning:
Praise be to Allah

2. Upon hearing this,his brother or companion should say to him,

Yarhamukallah

يَرْحَمُكَ اللهُ

Meaning:
May Allah bestow his Mercy on you

3. Upon hearing this, one who sneezed shall say to him,

Yahdheekumullahu wa yuslihu baalakum

يَهْدِيْكُمُ اللهُ وَيُصْلِحُ بَالَكُمْ

Meaning:
May Allah give you guidance and improve your condition
(Book: Bukhari 6224)