Is "He whose today is better than his yesterday is accursed" a Hadith, and what is its authenticity?

The wording mentioned in the question has not been found. However, something similar appeared in Al-Qari's Al-Mawḍū‘āt al-Kubrā with the wording: "Whoever has two days equal is cheated, and whoever has a day worse than his previous one is cursed." It was also said, "It is only known through a dream of Ibn Abī Rawwād." Similar to it is what Al-Daylamī narrated with a weak chain from ‘Alī, attributed to the Prophet: "Whoever has two days equal is cheated, and whoever has his latter day worse is cursed, and whoever is not increasing is in decrease, and for whoever is in decrease, death is better for him." In Kanz al-‘Ummāl, it is narrated from Al-Ḥasan ibn ‘Alī: "Whoever has his day balanced in it is deluded, and whoever has his day better than his morrow is cheated." These narrations are not authentically attributable to the Messenger of Allah, peace and blessings be upon him.