So Ashura was last month, a big Muslim fast day, which many compare to Yom Kippur, Tzom heAsor (the fast of the Tenth). But this is when Muslims fast to commemorate (at least according to Sunnis) the Splitting of the Sea. This is based on a tradition that Muhammad observed the Jews of Medinah fasting on this day and thought it was a good idea to memorialize the defeat of Pharaoh and salvation of the Israelites in this way. Now, Jews don’t fast on the seventh day of Passover, when we commemorate the Split, nowadays. But the Talmud (Pesahim 68b) cites R. Eliezer’s view that fasting is a viable option for holidays, and the prooftext is how the Torah talks about… the seventh day of Passover.

For it was taught, R. Eliezer said: A man has nought else [to do] on a Festival save either to eat and drink or to sit and study. R. Joshua said: Divide it: [devote] half of it to eating and drinking, and half of it to the study hall. Now R. Johanan said thereon: Both deduce it from the same verse. One verse says, ‘[Six days thou shalt eat unleavened bread: and on the seventh day] shall be a a solemn assembly to the Lord thy God’ (Deut. XVI, 8), whereas another verse says, ‘On the eighth day there shall be a solemn assembly unto you’ (Num. XXIX, 35): R. Eliezer holds: [That means] either entirely to God or entirely to you; while R. Joshua holds, Divide it: [Devote] half to God and half to yourselves.

Fascinating!