Nadav and Avihu the two older sons of Aaron died while serving incense and leaving out the Maaleh Ashan spice, they were previously warned about this Perek / Halacha: Yoma 1:5 Oz Vehadar / Artscroll: 10aVilna Shas: 7bAcademy of Hebrew Language: 566Venice / Bomberg: 39b