Dua when sneezing

One who sneezes should say:

Al-hum do lillâh

All praises are for Allah (SWT).

One who hears should respond by saying:

Yar-hamukallâh

Allah’s (SWT) mercy be upon you.

Then the sneezer should respond by saying:

Yah dikumullâhu wa yus-lihu bâlakum.

May Allah (SWT) guide you and reform your condition. (Bukhari)