Reference for Megillah 59:23

ולא פליגי הא דאיקלע ר"ח ניסן בשבת הא דאיקלע באמצע שבת:

There is no conflict [between these two statements]; the one refers to a case where Rosh Hodesh Nisan falls on Shabbat, and the other where it falls in the middle of the week.

Jastrow