Jami' at-Tirmidhi 3501

Anas narrated that the Messenger of Allah (ﷺ) said:

“Whoever says in the morning: ‘O Allah we have reached morning, calling You to witness, and calling the carriers of Your Throne to witness, and Your angels, and all of Your creation, that You are Allah, none has the right to be worshipped but You, Alone, without partner, and that Muhammad (ﷺ) is Your slave and Your Messenger. (Allāhumma aṣbaḥnā nush-hiduka wa nush-hidu ḥamalata `arshika wa malā’ikataka wa jamī`a khalqika bi-annaka Allāh, lā ilāha illā anta, waḥdaka lā sharīka laka, wa anna Muḥammadan `abduka wa rasūluk)’ Allah will forgive him for whatever he does that day, and if he says it in the evening, Allah will forgive him for whatever sin he commits that night.”