פירוש על ברכות 20:10

By "Samuel" is meant the Amora of that name. He taught that if the year is to be intercalated, it must be announced before the 30th of Adar, since witnesses might come to testify that the New Moon had been observed on that day, and it would accordingly be reckoned as the 1st of Nisan. Hezekiah, however, thought that the 30th of Adar could never be reckoned as the 1st of Nisan. He therefore intercalated the year on that day, which afterwards proved to be the New Moon, with the consequence that he observed the Passover in the second month instead of in the first.