"When one of you sneezes he should say:

الْحَمْدُ لِلَّهِ

All praises and thanks are to Allah.

Alhamdu lillaah

...and his brother or companion should say to him:

يَرْحَمُكَ اللَّهُ

May Allah have mercy upon you.

Yarhamukallaah

...and he [i.e. the one who sneezed] replies back to him:

يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُم

May Allah guide you and set your affairs in order.

Yahdeekumul-laahu wa yuslihu baalakum.

Al-Bukhari 7/125.