Sanhedrin 39a:14סנהדרין ל״ט א:י״ד
A certain heretic said to Rabbi Abbahu: Your God is a priest, as it is written: “That they take for Me an offering [teruma]” (Exodus 25:2), and teruma is given to the priests. He asked, sarcastically: When He buried Moses, in what ritual bath did He immerse? A priest who contracts impurity from a corpse must immerse in order to be able to partake of teruma. And if you would say that He immersed in water, but isn’t it written: “Who has measured the waters in the hollow of His hand” (Isaiah 40:12), that all waters of the world fit in the palm of God, so He could not immerse in them.
Tosafot on Sanhedrin 39a:14:1תוספות על סנהדרין ל״ט א:י״ד:א׳
"In what did He immerse?" -- the heretic did not ask, "how was He allowed to become impure [by burying Moshe]?". This is because the Jews are called children of God [and kohanim are allowed to become impure for their deceased children].
Chidushei Agadot on Sanhedrin 39a:10חידושי אגדות על סנהדרין ל״ט א:י׳
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Petach Einayim on Sanhedrin 39a:3פתח עינים על סנהדרין ל״ט א:ג׳
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Rosh David, Bo 26ראש דוד, בא כ״ו
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