The Prophet ﷺ said, "When one of you sneezes, let him say, 'Praise be to Allah,' and let his brother or companion say to him, 'May Allah have mercy on you.' When he says to him, 'May Allah have mercy on you,' let him reply, 'May Allah guide you and set your affairs right.'"
عن النبي ﷺ قال: إذا عطس أحدكم فليقل: الحمد الله، وليقل له أخوه أو صاحبه: يرحمك الله، فإذا قال له: يرحمك الله، فليقل: يهديكم الله ويصلح بالكم.
Bukhari reported it in Al-Adab (6224) from Malik bin Ismail, who said, Abdul-Aziz bin Abu Salama told us, Abdullah bin Dinar informed us, from Abu Salih, from Abu Hurairah, who mentioned it.