Invocation for sneezing

 188. When you sneeze , then say :

Alhamdu lillaah

All praises and thanks are to Allah.

Your companion should say :

Yarhamukallaah

May Allah have mercy upon you .

When someone says Yarhamukallaah to you then you should say:

Yahdeekumul-laahu wa yuslihu baalakum.

May Allah guide you and set your affairs in order.

Reference: Al-Bukhari 7/125.