Jami` at-Tirmidhi Book 43, Hadith 2
that the Messenger of Allah (ﷺ) said: "There are six things due from the believer to another believer: Visiting him when he is ill, attending (his funeral) to him when he dies, accepting his invitation when he invites, giving him Salam when he meets him, replying to him when he sneezes, and wishing him well when he is absent and when he is present."
that the Messenger of Allah (ﷺ) said: "There are six courtesies due from a Muslim to another Muslim: To give Salam to him when he meets him, to accept his invitation when he invites him, to reply to him when he sneezes, to visit him when he is ill, to follow his funeral when he dies, and to love for him what he loves for himself."
from Nafi: "A man sneezed beside Ibn 'Umar and said: 'Al-Hamdulillah Was-Salamu 'Ala Rasulillah. (All praise is due to Allah, and peace upon the Messenger of Allah)'. So Ibn 'Umar said: 'I too say Al-Hamdulillah Was-Salamu 'Ala Rasulillah, but this is not what the Messenger of Allah (ﷺ) taught us. He taught us to say: "Al-Hamdulillah 'Ala Kulli Hal (All praise is due to Allah in every circumstance)."