Prophet Muhhammad (SAW) said, A person who neglects a single fard Salat intentially, their name is written on the Gate of Hell. Which they must enter. Is this hadith authentic? Who narrated it?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The Prophetic narration to which you pointed in your question is reported by Imaam Abu Nu'aym that the Prophet said: "A person who deliberately neglects an obligatory prayer, his name will be written on the gate of Hellfire as one of those who will enter it." Then Abu Nu'aym said: "This narration is only reported by Saalih from Ismaa'eel (who are two narrators among the chain of narrators of the above narration"

This chain of narrators is weak as it contains Ismaa'eel Ibn Yahyaa At-Tameemi who is a liar, and he is classified as such by Ad-Daaraqutni, Ibn Hibbaan and others . For instance Ibn Hibbaan said about him: "He used to narrate fabricated narrations from trustworthy narrators, so it is not acceptable at all to report from him." Therefore, the narration with the chain of narrators that it mentioned is weak.

For more benefit on the ruling of abandoning the prayer, please refer to Fatwa 84390 and 87319.

Allaah Knows best.