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.
English: “And they had no children” — \ldots liable to death, as it is said “and Nadav and Avihu died, and they had no children.”
In context: The juxtaposition supplies the midrashic proof-text for the severity attached to one who leaves no offspring.
Custom
Chazal use the verse as a proof-text regarding the obligation of procreation.