26) From here we see that Cohanim do not make themselves tamei for the dead. For Elazar and Ithamar (the brothers of Nadav and Avihu) were Cohanim and they did not make themselves tamei for them. Who did make themselves tamei for them? The Levites (Mishael and Eltzafan).
Why Elazar and Ithamar Did Not Mourn Their Brothers
Sifra, Mekhilta deMiluim II 26
[כו] מכאן אמרו הכהנים אין מטמאין למתים שהרי אלעזר ואתמר כהנים היו ולא נטמאו להם. מי נטמאו להם? הלוים.