Sunnah & Manners relating to Sneezing
Noble Prophet Sallalahu Alaihi Wasallam has stated, “Allah azwajal likes the sneeze and does not like the yawn.” (Sahih Bukhari, pp. 163, vol. 4, Hadis. 6226)
The Holy Prophet Sallalahu Alaihi Wasallam has said, “When one sneezes and says "Alhamdu Lillah", the angels say "Rabul-‘Alamin" [Lord of the Universe] and if he [also] says, "Alhamdu Lillahi Rabbil Alamin" the angels say May Allah Taala have mercy upon you.” (Mu’jam Kabir, pp. 358, vol. 11, Hadis. 12284)
It is Sunnah to say "Alhamdu Lillah" after sneezing. It is better to say "Alhamdu Lillahi Rabbil Alamin". It is Wajib for the listener to say "Yarhamuk-Allah (may Allah have mercy on you)" immediately in an audible voice so that the one who sneezed can hear.
The reply is Wajib only when the one sneezing says "Alhamdu Lillah", if he does not say "Alhamdu Lillah" there is no reply. (Bahar-e-Shari’at, p. 120 vol. 16)
The Valiant, Companion Sayyiduna ‘Ali Radi Allahu Anhu said, ‘Whosoever says "Alhamdu Lillahi Rabbil Alamin Ala Kulli Haal" upon sneezing, his ears and jaw will never hurt.’ (Mirqa-tul Mafatih, pp. 499, vol. 8, Hadis. 4539).
Whosoever says "Alhamdu Lillahi Rabbil Alamin Ala Kulli Haal" after sneezing and rubs his tongue over all his teeth, Insha Allah Taala he will be safe from the various dental diseases. (Mira-tul Manajih, p. 396 vol. 6)
Listener to say "Alhamdu Lillah" before the one who sneezed, HE/SHE will be protected from Waist/ Back pain and ear pain and also protected from Indigestion.
If a non-Muslim sneezes and says "AL-HAMDU-LILLA" one should reply and say "yah'deekumullah" meaning May Allah Azwajal guide you. It is not compulsory to reply to a non-Muslim
May Allah Taala give us the ablity to Follow the sweet Acts set by our Madani Aqa Sayyedina Muhammad Mustufa Sallalahu Alaihi Wasallam. - Ameen.