chasidut hasidism - The Noam Elimelech: "G-d is refereed to as a Kohen"- What's the source?

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?

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_{¹ Additionally see the Noam Elimelech in Parshas Tazria where he refers to this idea as well}

Answer

Talmud Bavli Zevachim 101b-102a תלמוד בבלי זבחים קא עמוד ב - קב עמוד א

מיתיבי מרים מי הסגירה א"ת משה הסגירה משה זר הוא

When Miriam became a leper (see Numbers 12:10), who diagnosed and quarantined her? If you say that Moses quarantined her, that is difficult, as Moses was a non-priest,

102a

ואין זר רואה את הנגעים וא"ת אהרן הסגירה אהרן קרוב הוא ואין קרוב רואה את הנגעים

and a non-priest may not inspect the shades of leprous marks to diagnose them. And if you say that Aaron quarantined her, that is difficult, as Aaron was a relative, Miriam’s brother, and a relative may not inspect the shades of leprous marks.

אלא כבוד גדול חלק לה הקב"ה למרים אותה שעה אני כהן ואני מסגירה אני חולטה ואני פוטרה

Rather, the Holy One, Blessed be He, bestowed a great honor on Miriam at that time, and said: I Myself am a priest, and I will quarantine her for seven days to see if the shades of leprous marks persist, and I will declare her a leper if she is impure, and I will exempt her if she is not impure.