Riyad us Saliheen: Hadith 879

The Prophet (ﷺ) said, "When one of you sneezes he should say: 'Al-hamdu lillah (praise be to Allah),' and his brother or his companion should say to him: 'Yarhamuk-Allah (may Allah have mercy on you).' When he says this he should reply: 'Yahdikum-ullah wa yuslihu balakum (may Allah guide you and render sound your state of affairs)."'

[Al- Bukhari].