Amr Ibne shoaib has polyquoted his father and the Holy Prophet of Islam (SAW) as saying:
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“While being happy and having a smile on his lips, Gabriel come down from heaven to the Holy Prophet (SAW) bringing the following Dua saying: God has sent a gift for you. 

The Holy Prophet said: What is the gift O Gabriel!

Gabriel said: Words along with treasures of heaven by which God has honoured you. 

The Holy Prophet said: What are those words O Gabriel?!

Gabriel said: Say: “O You who reveal beauty and conceal ugly things! O You who do not take a wrongdoer to task and not tear the veil! O You who are Great Forever! O You who have the great forbearance! O You who have pardon abounding! O You who have opened Your hands for mercy! O Hearer of all whisperings! O You to whom all complaints are made! O Noble face! O Possessor of great favor! O You who give blessings to Your servants when they do not deserve it! O our Master! O our Lord! O our Guardian! O the Goal of our desires! I beseech You O God! not to make my being ugly with Fire.”

“Here the Holy Prophet (SAW) said to Gabriel: What is the virtue of these words?  Gabriel said: Far away! Far away! It is something impossible, for if the angels of seven heavens and seven earths gather to describe its virtues till the Day of Judgment, they are not able to describe a single part of it.”
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  “Therefore when a man says: O You who reveal the beauty and conceal the ugly, God covers up his defects and has mercy on him and makes him look beautiful on the Day of Judgment and covers his defects with a thousand veils in the world and the hereafter.”
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  “And when he says: O You who do not take the wrongdoer to task and do not tear the veil, God will not take him to task on the Day of Judgment and on the day all veils are torn, God will not tear his veil.”
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  “And when he says: O You who are Great Forgiver, God will forgive his sins even if they are as much as the sea foam.”
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  “And when he says: O You are of great forbearance, God will forgive him such sins as theft, drinking wine, and other sins.”
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  “And when he says: O You who have pardon abounding, God will open seventy gates of Mercy to him in a way that he will be overwhelmed by God’s Mercy till he dies.”
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  “And when he says: O You who have opened Your hands for mercy, God opens His hands of Mercy to him.”
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  “And when he says: O Hearer of all whisperings, O You to whom all complaints are made, God will give him rewards as many as given to every afflicted and unaffiliated, every losing and sick as well as destitute and every one affected by calamity till the Day of Judgment.”
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  “And when he says:  O Possessor of great favor, God will make him noble as prophets.”
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  “And when he says: O You who give blessings to Your servants when they do not deserve it, God will grant him rewards as many as the number of those who have thanked His blessings.”
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  “And when he says: O our Master, O our Lord, God will say: My angels! Be witness that I forgave him and I will give him rewards as many as those being in paradise and Hell, the seven heavens and the earths, the sun, the moon, the stars, drops of rain, sands mountains, dews and throne.”
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  “And when he says: O our Guardian, God will make his heart replete with faith.”
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  “And when he says: O the Goal of our desires, God will give him the love of all creatures on the Day of Judgment.”
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  “And when he says: I beseech You O God not to make my being ugly with Fire, God will say: My servant has asked Me to free him from Fire.  O My angels! Be witness that I set him, his parents, his brothers, his household, his children and his neighbors free from the Fire and accepted his intercession for a thousand others who deserved the punishment by fire and saved them from it.”
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  _ “O Muhammad! Teach this Dua only to men of piety.  Do not even teach it to hypocrites, for it is a Dua which God will answer.  This is the Dua recited by the men of Beite Ma’moor (an edifice in the fourth or seventh heaven as sacred as Ka’aba) when they circumambulate it.”

Praise is due to Allah,
the One and His greetings and peace on Muhammad and his progeny.