Sunan Ibn Majah Book 34, Hadith 21
the Messenger of Allah (saas) said to a man: "What do you say during your prayer?" He said: "I recite the Tashah-hud then I ask for Allah for Paradise and see refuge with Him from Hell, but by Allah I do not understand your whispering or the whispering of Mu'adh." He said: "It is concerning them (Paradise and Hell) that we are whispering."
the Messenger of Allah (saas) taught her this supplication: "Allahumma inni as'aluka minal-khayri kullihi, 'ajilihi wa ajilihi, ma 'alimtu minhu wa ma la a'lam. Wa a'udhu bika minash-sharri kullihi, 'ajilihi wa ajilihi, ma 'alimtu minhu wa ma la a'lam. Allahumma inni as'aluka min khayri ma sa'alaka 'abduka wa nabiyyuka, wa a'udhu bika min sharri ma 'adha bihi 'abduka wa nabiyyuka. Allahumma inni as'alukal-jannatah wa ma qarrab ilayha min qawlin aw 'amalin, wa a'udhu bika minan-nari wa ma qarraba ilayha min qawlin aw 'amalin, wa as'aluka an taj'al kulla qada'in qadaytahuli khayran (O Allah, I ask You for all that is good, in this world and in the Hereafter, what I know and what I do not know. O Allah, I seek refuge with You from all evil, in this world and in the Hereafter, what I know and what I do not know. O Allah, I ask You for the good that Your slave and Prophet has asked You for, and I seek refuge with You from the evil from which Your slave and Prophet sought refuge. O Allah, I ask You for Paradise and for that which brings one closer to it, in word and deed, and I seek refuge in You from Hell and from that which brings one closer to it, in word and deed. And I ask You to make every decree that You decree concerning me good)."
"A man come to the Prophet (saas) and said: 'O Messenger of Allah, what supplication is best?' He said: 'Ask your Lord for forgiveness and to be kept safe and sound in this world and in the Hereafter.' Then (the man) came the next day and said: 'O Messenger of Allah, what supplication is best?' He said: 'Ask your Lord for forgiveness and to be kept safe and sound in this world and in the Hereafter.' Then (the man) came the third day and said: 'O Prophet of Allah, what supplication is best?' He said: 'Ask your Lord for forgiveness and to be kept safe and sound in this world and in the Hereafter, for if you are forgiven and kept safe and sound in this world and the Hereafter, you will have succeeded.'"