The Prophet ﷺ said, "There is no Muslim, or human being, or servant who says when he reaches the evening and when he reaches the morning, 'I am content with Allah as my Lord, with Islam as my religion, and with Muhammad as my Prophet,' except that it becomes a right upon Allah to make him content on the Day of Resurrection."
حدثنا أبو بكر بن أبي شيبة حدثنا محمد بن بشر حدثنا مسعر حدثنا أبو عقيل عن سابق
عن النبي ﷺ قال ما من مسلم أو إنسان أو عبد يقول حين يمسي وحين يصبح رضيت بالله ربا وبالإسلام دينا وبمحمد نبيا إلا كان حقا على الله أن يرضيه يوم القيامة
[Its isnad is hasan] Tabarani narrated it, 22/367, no. 621, from the hadith of Ibn Abu Shayba with the same wording, and it is found in al-Musannaf, 10/240, 241. Abu Dawud also narrated it, in the Book of Manners, chapter on what one says when morning comes, no. 5072, from the hadith of Abu Salam, from a servant of the Prophet ﷺ, and this is the correct version. Hakim declared it sahih, 1/518, as did Dhahabi, and the error came from Masaar, may Allah have mercy on him. And Allah knows best.