Say to the one who sneezes:
يَرْحَمُكَ اللَّهُ
Yarhamuka Allahu!
“May Allah have mercy on you”.
The person sneezing should then reply
يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُمْ
Yahdeekumu Allahu wa yuslihu baalakum!
“May Allah keep you on hidayat (guidance) and make proper your condition. (Mishkat, Bukhari)
If the sneezing person is a woman, the reply is with a kasrah (zer) on the kaaf. (Mishkat)