Abdullah ibn Amr ibn al— As, may Allah be pleased with him and his father, said,
“Five things, he who embodies them will be happy in this world and in the next:
The first is to regularly say, ‘La ilaha illa Allah, Muhammadun rasululAllah’ — There is no god but ALLAH, & Muhammad is the Messenger of ALLAH.
The second is to say when inflicted with a calamity, ‘Inna lillahi wa innailayhi raji un, wa la hawla wa la quwwata illa billahil alliyyil atheem’ —Verily we belong to Allah and to Him we shall all return, and there is no power or might except by the will of Allah the most High, the Mighty.
The third is to say in gratitude when giving a blessing, ‘Al—hamdu lillahiRabbil alamin’ — Praise be to Allah, Lord of the Universe.
The fourth is to say when beginning anything, ‘Bismillahir RahmanirRahim’ – In the name of Allah The Most Gracious The Most Merciful.
And the fifth is to say upon committing a sin, ‘Astaghfiru llahil atheemawa atubu ilayh’ — I seek the forgiveness of Allah the Greatest and Irepent to Him.”
Ref: [Ibn Hajr Al—Asqalani in, ‘Preparing For The Day Of Judgement’,Chapter 4: “Counsel In Fives”, Qt.(8)]