Bismillahi tawakkaltu 'ala Allahi wa la hawla wa laa quwwata illa billah!
"I depart with Allah's name, relying on Him. It is Allah who saves us from sins with His guidance (the ability to do so)." (Tirmidhi)
It is stated in the hadith that if a person recites the above dua and departs then there is an (unseen) proclamation that his/her need will be fullfilled and that he will be protected from any harm or injury. On hearing this dua, the Satan goes away from the place and refrains from troubling the reciting person. (Tirmidhi)
Allahumma inni a'udhu bika min an adilla aw udalla aw adhlima aw udhlama aw ajhila aw yujhala 'alayya
"O Allah, I seek refuge in You from misleading or being misled or oppressing or being oppressed or from being ignorant or bearing the result of ignorance".(Mishkat)
When hearing someone sneeze
Say to the one who sneezes:
يَرْحَمُكَ اللَّهُ
Yarhamuka Allahu!
"May Allah have mercy on you".
The person sneezing should then reply
يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُمْ
Yahdeekumu Allahu wa yuslihu baalakum!
"May Allah keep you on hidayat (guidance) and make proper your condition. (Mishkat, Bukhari)
If the sneezing person is a woman, the reply is with a kasrah (zer) on the kaaf. (Mishkat)
Ash-hadu an laa ilaha illa Allahu wahdahu laa shareeka lahu wa ash-hadu anna Muhammadan 'abduhu wa rasuluh!
"I testify that there is no one worthy of worship besides Allah. He is all by Himself and has no partner and I testify that Muhammad is Allah's Rasul (Messenger)".
Eight doors of Jannah will be open for the reciter of this dua. He will be able to enter from whichever door he pleases. (Mishkat)
It is recorded in the same narration that the dua should be recited three times. (Hisnul Hasin)
Subhanaka Allahumma wa bi-hamdika ash-hadu an laa ilaaha illaa anta astaghfiruka wa atubu ilayka!
"O Allah, You are pure, I praise You and testify that only You are worthy of worship and I seek forgiveness from You (I turn to You for forgiveness).
(Hisnul Hasin, from Mustadrak)