It was proven in the hadeeth of Abu Hurayrah (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said:
“Allaah likes the act of sneezing and dislikes the act of yawning, so if any one of you sneezes and praises Allaah (says “al-hamdu Lillaah”), it is a duty on every Muslim who hears him to say to him, “Yarhamuk Allaah (may Allaah have mercy on you).” As for yawning, it is from the Shaytaan, so if any of you feels the urge to yawn, he should suppress it as much as he can, for when any one of you yawns, the Shaytaan laughs at him.”
(Reported by al-Bukhaari, 10/505)
What to Do when you Sneeze
It was also reported from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said:
“If any one of you sneezes, let him say ‘Al-hamdu Lillaah,’ and let his brother or his companion say, ‘Yarhamuk Allaah.’ And if he says to him, ‘Yarhamuk Allaah,’ let him say, ‘Yahdeekum Allaahu wa yusliha baalakum (May Allaah guide you and correct your thinking).’”
(Reported by al-Bukhaari, 10/502)
Also among the manners of sneezing is covering the mouth with hand or piece of cloth and suppresing the sound.
Abu Hurairah (May Allah be pleased with him) reported:
Whenever the Messenger of Allah (ﷺ) sneezed, he would cover his mouth with his hand or a piece of cloth, suppressing the sound this way.
[Abu Dawud and At-Tirmidhi]
What if Someone sneezes and does not say Alhamdulillah
Anas (may Allaah be pleased with him) reported that
two men sneezed in the presence of the Prophet (peace and blessings of Allaah be upon him), who said “Yarhamuk Allaah” to one of them, but not to the other. The one to whom he did not say it said: “So and so sneezed, and you said ‘Yarhamuk Allaah’ to him; I sneezed but you did not say it to me.” He said, “He praised Allaah (said ‘al-hamdu Lillaah’) and you did not.”
(Reported by al-Bukhaari, 10/504)
If a person sneezes several times in a row, when is it prescribed to say “Yarhamuk Allah” to him?
A man sneezed in the presence of the Messenger of Allah (blessings and peace of Allah be upon him) whilst I [the narrator] was watching, and the Messenger of Allah (blessings and peace of Allah be upon him) said: “Yarhamuk Allah.” Then the man sneezed a second or third time and the Messenger of Allah (blessings and peace of Allah be upon him) said: “Yarhamuk Allah, this is a man who has a cold.”
At-Tirmidhi said: A saheeh hasan hadeeth.
And it was narrated that Salamah ibn al-Akwa‘ (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said:
“The one who sneezes may be told Yarhamuk-Allaah three times; if he sneezes more than that, he has a cold.”
Narrated by Ibn Maajah (3704); classed as saheeh by al-Albaani in Saheeh Sunan Ibn Maajah.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: Is it obligatory to say “Yarhamuk Allah” to one who sneezes once, and if he sneezes three times to repeat that three times or more?
He replied: If he sneezes three times and you say “Yarhamuk Allah” each time, then after the third sneeze you should say to him: “ ‘Aafaaka Allah(may Allah grant you well-being); because that is a cold, so say: May Allah grant you well-being; you have a cold. All you have to say is: May Allah grant you well-being, and you may add: You have a cold.
from Liqa’ al-Baab al-Maftooh, no. 127
May Allah help us in following the Sunnah.Ameen.