These are confirmed Sunnahs of the Prophet.
Responding to the one who sneezes.
Abu Hurairah (may Allah be pleased with him) narrated
that the Prophet (peace and blessings of Allah be upon him) said:
"When one of you sneezes, let him say: 'Al-hamdu lillah' (Praise be to Allah).
And his brother or companion should say to him:
'Yarhamuk-Allah' (May Allah have mercy on you).
And when he says to him: 'Yarhamuk-Allah,'
he should reply: 'Yahdeekum-Allah wa yuslihu balakum' (May Allah guide you and set your affairs right)."
Narrated by al-Bukhari.