TT #50 · Parshas Shemini · Aliyah 3 · Passuk 6
Chabad.org — Vayikra Chapter 10 with Rashi
English: “And your brethren, the whole house of Israel, shall bewail the burning”: when Rabbi Yishmael’s sons died, Rabbi Tarfon applied this verse to comfort him, reasoning that if Nadav and Avihu, who performed only one mitzvah, were mourned by all Israel, Rabbi Yishmael’s sons certainly warranted such mourning.
Moed Katan 28b.
E-Daf.com — Moed Katan 28b (Tsurras Hadaf)
Kal vachomer — if the death of Nadav and Avihu, who performed only one mitzvah, warranted the mourning of the whole house of Israel, the deaths of Rabbi Yishmael’s sons warranted mourning all the more.
The verse is invoked in the consolation of Rabbi Yishmael after the death of his sons, drawing a comparison to the mourning for Nadav and Avihu and emphasizing the grief due to righteous people.