Authentic Supplication Number 235.

It is reported that the Prophet  said: "If one of you sneezes let him say:Al-hamdu lil-lahi and let his brother or companion say to him: Yarhamuka 'allahu (241) then if he says Yarhamuka 'allahu, let him say:Yahdeekumu 'allahu wayuslih balakumu (242) and in one narration: Al-hamdu lil-lahi `ala kulli halin (243)

Footnotes.
(241) May Allah have mercy on you.
(242) May Allah guide you and better your affairs.
(243) All praise is to Allah upon all circumstances.

Reporters.
Reported by Al-Bukhari and is #162 in The Authentic of Good Sayings.