Parashas Bamidbar · Passuk 3:04
But Nadab and Abihu died by GOD’s will,aby GOD’s will Lit. “before GOD.” when they offered alien fire before GOD in the wilderness of Sinai; and they left no sons. So it was Eleazar and Ithamar who served as priests in the lifetime of their father Aaron.
Chabad.org — English translation + Rashi
Source: Sanhedrin 52a.
E-Daf.com — Tsurras Hadaf (size=3)
English: “And they had no children” — it was taught: Abba Chanan in the name of R’ Elazar: Anyone who does not engage in being fruitful and multiplying is liable to death.
In context: The death of Nadav and Avihu without offspring is linked to the broader obligation of procreation; the midrash treats childlessness in this context with severity.
Custom
Chazal connect the note that Nadav and Avihu had no children to the gravity of neglecting the mitzvah of procreation.