Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Whoever recites this in the morning:
'Allahumma inni asbahtu ushhiduka, wa ushhidu hamalata 'arshika, wa mala'ikataka, wa jami'a khalqika, bi-annaka anta wahdaka la sharika lak, wa anna Muhammadan 'abduka wa rasuluk' (O Allah, I have entered the morning, calling You to witness, and calling to witness the bearers of Your Throne, Your angels and all Your creation, that there is no god other than You; You alone are God, You have no partner, and that Sayyiduna Muhammad (peace and blessings be upon him) is Your servant and Your Messenger).
The Prophet (peace and blessings be upon him) says: Allah Almighty forgives that person whatever sin he has committed during that day, and if that person recites these words in the evening, Allah Almighty forgives that person his sins of that night."
(Allamah al-Haythami says:) I say: Shaykh al-Islam al-Mizzi attributed this report in his book al-Atraf to the narration of Ibn Dasah from Imam Abu Dawud, and he also attributed it to Imam al-Tirmidhi. Likewise, he attributed the narration of Makhul from Sayyiduna Anas (may Allah be pleased with him) with this text to Imam Abu Dawud. When I examined this, the text of the report narrated by Makhul contains these words: "O Allah, You are my Lord; there is no god other than You." I did not find this report in the copy I have, so I feared that some error might have entered the report narrated by Muslim bin Ziyad, just as it had entered the report narrated by Makhul; so I recorded this report.
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains a narrator, Baqiyyah bin al-Walid, who is a mudallis (one who conceals defects in the chain).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 17016