When Beis din proclaims the day of Rosh Chodesh, even if the eidim turn out to be זוממים the day remains קדוש | Kiddush HaChodesh 2:2

When Beis din proclaims the day of Rosh Chodesh, even if the eidim turn out to be זוממים the day remains קדוש | Kiddush HaChodesh 2:2