Genesis 14:19–20; such a precedence is not befitting a priest who should totally serve God (Eitz Yosef to Leviticus Rabbah 25:6)
Rabbi Zechariah, quoting Rabbi Ishmael; Leviticus Rabbah 25:6; Babylonian Talmud, Nedarim 32b; Zohar, 1:86b. The text says of Melchizedek "and he was a priest" (Genesis 14:18), meaning him personally and not his descendants.(Ohr HaChayim to Genesis 14:18 (first explanation). Eitz Yosef commentary to Leviticus Rabbah 25:6. Zohar vol. 1 p. 86b)
