From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer dismisses the debate between thirteen and three principles of faith as a mere naming dispute with no practical consequence. He argues that belief in future redemption cannot be an independent foundational principle, since our obligation to serve God is unconditional. Nevertheless, he rules that one who denies the redemption is a heretic, because it is explicitly stated in the Torah and Prophets, and denying any Torah passage constitutes denial of the fundamental principle of Torah from Heaven.
Source: Shu"t Chasam Sofer YD §356