משנה אויף שמות 34:19

[An Israelite] who buys a fetus of a donkey belonging to a non-Jew or who sells one to him, although this is not permitted, or who forms a partnership with him, or who receives [an animal] from him to look after or who gives [his donkey] to him to look after, is exempt from the [law of the] bekhor, for it says: [“I sanctified to me all the firstborn] in Israel,” (Numbers 3:13) but not in non-Jews. Priests and levites are exempt through [an argument made by a] kal vehomer: if they exempted the first-born belonging to the Israelites in the wilderness, it follows all the more so that they should exempt their own.

These may be given to any priest:Devoted things (haramim); Firstlings; The redemption of the first born; The [lamb substituted as] ransom for the firstling of a donkey; The shoulder, the two cheeks and the maw; The first of the fleece; Oil [fit only] for burning; Consecrated food [which must be eaten] within the Temple; And bikkurim. Rabbi Judah prohibits bikkurim. Vetches of terumah: Rabbi Akiva permits, But the sages prohibit.