Gemara:

Pesachim 

Halacha:

Pesach,  Shabbat 

Machshava:

Pesach,  Shabbat 

References: Pesachim: 66A ,  Shabbat: 87B ,  Shabbat: 31A  

Description

The famous story about how the Jewish people "forgot" the Halchot of Korban Pesach when Erev Pesach falls on Shabbat ACTUALLY teaches the sheer power of a Jew, if they just try, to fix and not mess up even messy situations