Whenever a believer sneezes, it is desirable to praise Allah Almighty by saying the following words:
Alhamdulillah – All praises is due to Allah
Then it becomes incumbent upon the adjacent listeners to respond by saying the following words:
Yar Hamu Kallah – May Allah show mercy to you.
Abu Musa al-Ashari narrated that Nabi Muhammad (Sall Allahu Alayhi Wasallam) said: “When one of you sneezes and praises Allah, respond to him and in case he does not praises Allah do not respond to him.” (Muslim)
Yawning is a devilish act. Whenever a man yawns, he should cover his mouth with hands or hand kerchief. It is essential to check the entry of something injurious into the mouth.
It is reported on the authority of Abu Hurairah (Radhiy Allahu Anhu) that Nabi Muhammad (Sall Allahu Alayhi Wasallam) said: “Allah likes sneezing and detests yawning. So when one of you sneezes and praises Allah, it becomes obligatory upon every Muslim to say: “May Allah be kind to you.” As for yawning it is surely from the devil; so whosoever yawns, let him return it if it is possible; for the yawner is mocked at by the devil.”