1,252. Who Is Believed

Hilchos Kiddush HaChodesh 3:13

The messengers for Nisan travel two days longer than the messengers for Tishrei. This is because the messengers for Tishrei don’t travel on 1 Tishrei, which is Rosh Hashana, or on 10 Tishrei, which is Yom Kippur.

Hilchos Kiddush HaChodesh 3:14

Two messengers are not necessary because even a lone messenger is believed. This doesn’t only apply to the messengers. Even if a merchant of no great standing passes through an area and says that he heard from the court that they sanctified the new month on a particular day, his statement is believed and the holidays are scheduled accordingly. The dates of Rosh Chodesh and the holidays would become common knowledge soon enough, so the testimony of a single valid witness is enough.