A Beautiful Hadith and a Dua

Narrated Anas ibn Malik: The Prophet (peace_be_upon_him) said:

“If anyone says in the morning:

“O Allah!

In the morning we call Thee, the bearers of Thy Throne, Thy angels, and all Thy creatures to witness that Thou art Allah than Whom there is no god, Thou being alone and without a partner, and that Muhammad is Thy servant and Thy Apostle,”

Allah will forgive him any sins that he commits that day; and if he repeats them in the evening. Allah will forgive him any sins he commits that night.

Abu Dawud (Book #41, Hadith #5060)

“اللَّهُمَّ إِنِّي أَصْبَحْتُ أُشْهِدُكَ وَأُشْهِدُ حَمَلَةَ عَرْشِكَ، وَمَلَائِكَتَكَ وَجَمِيعَ خَلْقِكَ، أَنَّكَ أَنْتَ اللهُ لَا إِلَهَ إِلَّا أَنْتَ وَحْدَكَ لَا شَرِيكَ لَكَ، وَأَنَّ مُحَمَّداً عَبْدُكَ وَرَسُولُكَ”.

 Allaahumma ‘innee ‘asbahtu ‘ush-hiduka wa ‘ush-hidu hamalata ‘arshika, wa malaa’ikataka wajamee’a khalqika, ‘annaka ‘Antallaahu laa ‘ilaaha ‘illaa ‘Anta wahdaka laa shareeka laka, wa ‘anna Muhammadan ‘abduka wa Rasooluka.

O Allah , I have entered a new morning ¹ and call upon You and upon the bearers of Your Throne , upon Your angels and all creation to bear witness that surely You are Allah , there is none worthy of worship but You alone , You have no partners, and that Muhammad is Your slave and Your Messenger . (Recite four times in Arabic.) ²

Reference:
¹ When you say this in the evening you should say, Allaahumma ‘innee ‘amsaytu. . . .: “O Allah, I have ended another day…”
² ”Allah will spare whoever says this four times in the morning or evening from the fire of Hell, ” Abu Dawud 4/317. It was also reported by Al-Bukhari in Al-’Adab Al-Mufrad, An-Nasa’i in ‘Amalul-Yawm wal-Laylah and Ibn As-Sunni. Nasa’i's and Abu Dawud’s chains of transmission are good (Hasan), Ibn Baz, p. 23.