1) If anyone of you sneezes, he should say 'Al Hamdu Lillah' (Praise be to Allah), and
2) His (Muslim) brother or companion should say to him, 'Yar Hamu Kallah' (May Allah bestow his Mercy on you).
3) When the latter says 'Yar hamu kallah", the former should say, 'Yahdi Kumul Laahu Wa Yuslihu Baalakum' (May Allah give you guidance and improve your condition).

PROPHET MUHAMMAD (ﷺ) said:
1) When one of you sneezes let him say: 'Al Hamdu Lillahi Alaa Kulli Haal (All praise is due to Allah in every circumstance).'
2) And let the one replying to him say: 'Yar Hamu Kallah (May Allah have mercy upon you).'
3) And let him say to him: 'Yahdi Kumul Laahu Wa Yuslihu Baalakum'(May Allah guide you and rectify your affairs).'"

It was narrated from AbU Burdah that his father said: "The Jews used to sneeze in the presence of the Prophet , hoping that he would say to them, 'Yar Hamu Kallah" (May Allah have mercy on you),' but he used to say: 'Yahdi Kumul Laahu Wa Yuslihu Baalakum (May Allah guide you and
set your affairs straight)."