Gemara:

Megillah 

Halacha:

Beit HaKenesset,  Purim,  Tefillah 

References: Megilla: 14A ,  Megilla: 21A  

Description

If Megilla reading is in place of Hallel, why don't we stand for the duration of reading it, as we must do each time we say Hallel? Four possible answers as to why the law is clear that you can sit.