Rashi on Deuteronomy 14:8/רש"י על דברים י״ד:ח׳

1ובנבלתם לא תגעו YE SHALL NOT TOUCH THEIR CARRION — Our Rabbis explained that this refers only to the festive seasons when every male Israelite was obliged to appear in the Sanctuary and should therefore be in a state of cleanness. One might think that they (the Israelites, i.e. non-priests) are prohibited from touching a carcass during the whole year! It, however, states, (Leviticus 21:1) in reference to the uncleanness of a corpse: “Say unto the priests … [there shall none be defiled by the dead] etc.”. Now you may draw a conclusion a fortiori: How is it in the case of uncleanness caused by a corpse which is a stringent kind of uncleanness? Priests only are prohibited regarding it but ordinary Israelites are not prohibited! Surely in the case of uncleanness caused by a carcass which is less stringent this is all the more so! (Sifra, Shemini, Chapter 4 8-9; cf. Rashi on Leviticus 11:8 and Note thereon).