The Noam Elimelech in his first piece in Parshas Metzora writes:
(Source from Sefaria.org)
"ביום טהרתו והובא אל הכהן", פירוש ביום שיטוהר מעוונו יפעול להעלות השכינה ליחדה עם קב"ה, וזהו "והובא אל הכהן", הקב"ה נקרא כהן,
"And on the day of his [the Metzora's] purification he shall be brought to the Kohen" (Lev.14:2), meaning on the day which he is purified from his sin and he will act to elevating the Shechina and unite it with the Holy One, blessed be He; This is "And he shall be brought to the Kohen"- G-d is called "[a] Kohen" 1
Where is this idea of G-d being reffered to as "a Kohen" appear originally? Is this the Noam Elimelech's own novel idea or is this idea based in Tanach, Chazal or Zohar?
1 Additionally see the Noam Elimelech in Parshas Tazria where he refers to this idea as well