What is "Beis Nisroch"?
Rashi (from Sanhedrin 96a): It is a Neser (board) from Noach's ark. Ba'al ha'Turim - Ararat is mentioned only here (and this verse is repeated in Melachim II, 19:37) and regarding No'ach (Bereishis 8:4).
Why did his sons kill him?
Rashi (from Sanhedrin 96a): He said, if I am saved from the nobles, whose sons died through me (in my camp) I will sacrifice my two sons to [the board]. His sons heard this.
Radak (Melachim II, 19:37, from Tanchuma Vayikra 8): Sancheriv asked his Chachamim why Hashem loves Yisrael so much. They said, their patriarch was willing to sacrifice his son to Hashem. He said, I will offer my two sons to Him 1 ! They heard.
This is not in the Buber edition of the Midrash. The Warsaw edition says that he offered his Bechor - "va'Yikach Es Bno
