According to a hadith in At-Tirmithi, the Prophet (saws) recommended this dua for the day of Arafat
Laa 'ilaaha 'illallaahu wahdahu laa shareeka lahu, lahul-mulku wa lahul-hamdu wa Huwa 'alaa kulli shay'in Qadeer.
None has the right to be worshipped but Allah alone, Who has no partner. His is the dominion and His is the praise, and He is Able to do all things.
Today would also be a good day to re read the Prophet's last sermon, which was delivered today at Arafat in the year 10 A.H., or 632 A.D.
"O People, listen well to my words, for I do not know whether, after this year, I shall ever be amongst you again. Therefore listen to what I am saying to you very carefully and take these words to those who could not be present today.
O People, just as you regard this month, this day, this city as Sacred, so regard the life and property of every Muslim as a sacred trust. Return the goods entrusted to you to their rightful owners. Treat others justly so that no one would be unjust to you. Remember that you will indeed meet your LORD, and that HE will indeed reckon your deeds. God has forbidden you to take usury (riba), therefore all riba obligation shall henceforth be waived. Your capital , however, is yours to keep. You will neither inflict nor suffer inequity. God has judged that there shall be no riba and that all the riba due to `Abbas ibn `Abd al Muttalib shall henceforth be waived.
Every right arising out of homicide in pre-Islamic days is henceforth waived and the first such right that I waive is that arising from the murder of Rabi`ah ibn al Harith
ibn `Abd al Muttalib.
O Men, the Unbelievers indulge in tampering with the calendar in order to make permissible that which God forbade, and to forbid that which God has made permissible. With God the months are twelve in number. Four of them are sacred, three of these are successive and one occurs singly between the months of Jumada and Sha`ban. Beware of the devil, for the safety of your religion. He has lost all hope that he will ever be able to lead you astray in big things, so beware of following him in small things.
O People, it is true that you have certain rights over your women, but they also have rights over you. Remember that you have taken them as your wives only under God's trust and with His permission. If they abide by your right then to them belongs the right to be fed and clothed in kindness. Treat your women well and be kind to them, for they are your partners and committed helpers. It is your right and they do not make friends with anyone of whom you do not approve, as well as never to be unchaste...
O People, listen to me in earnest, worship God (The One Creator of the Universe), perform your five daily prayers (Salah), fast during the month of Ramadan, and give your financial obligation (zakah) of your wealth. Perform Hajj if you can afford to.
All mankind is from Adam and Eve, an Arab has no superiority over a non-Arab nor a non-Arab has any superiority over an Arab; also a white has no superiority over a black nor a black has any superiority over white except by piety and good action. Learn that every Muslim is a brother to every Muslim and that the Muslims constitute one brotherhood. Nothing shall be legitimate to a Muslim which belongs to a fellow Muslim unless it was given freely and willingly. Do not, therefore, do injustice to yourselves. Remember, one day you will appear before God (The Creator) and you will answer for your deeds. So beware, do not stray from the path of righteousness after I am gone.
O People, no prophet or messenger will come after me and no new faith will be born. Reason well, therefore, O People, and understand words which I convey to you. I am leaving you with the Book of God (the Quraan) and my Sunnah (the life style and the behavioral mode of the Prophet), if you follow them you will never go astray.
All those who listen to me shall pass on my words to others and those to others again; and may the last ones understand my words better than those who listen to me directly. Be my witness O God, that I have conveyed your message to your people.