Ibn Ezra on Numbers 28:11

ובראשי חדשיכם. אמר רבי משה הכהן הספרדי נ"ע שפירושו חדש ניסן כי כן כתוב ראשון הוא לכם ואחר כן אמר זאת עולת חדש בחדשו שיעשו כן בכל חדש על כן הוסיף לחדשי השנה ופירושו נכון הוא ואע"פ שיש לטעון על יו"ד ובראשי חדשיכם רק בעבור שמצאנו הנה חדש מחר ישר דבורו: AND IN YOUR NEW MOONS. Rabbi Moses Ha-Kohen the Spaniard, who rests in paradise, says that u-ve-roshe chodshekhem¹⁸Literally, and in the first of your months. Hence Rabbi Moses’ interpretation. (and in your new moons) refers to the new moon of Nisan, for Scripture clearly states, it shall be the first month of the year to you (Ex. 12:2).¹⁹Hence the first of your months (see previous note) refers to the first month of the year, i.e., the new moon of Nisan. Scripture then goes on to say, This is the burnt-offering of every new moon (v. 14), that is, they shall offer this burnt offering²⁰The same burnt offering that was offered on the new moon of Nisan. on every new moon. The Torah therefore adds, throughout the months of the year (Ibid.).²¹A similar burnt offering shall be offered on the new moons throughout the year. Rabbi Moses’ interpretation is correct. He is right even though the yod in u-ve-roshe chodshekhem (and in your new moons) argues against his interpretation.²²Roshe is a plural. Hence roshe chodshekhem seems to mean the many first days of the month. If the reference was to the new moon of Nisan, then Scripture should have read u-ve-rosh chodshekem (and on the first day of your months). However, the fact that we find hinneh chodesh machar²³Not hinneh rosh chodesh machar. (Behold, tomorrow is the new moon) (I Sam. 20:5) shows that what he says is correct.²⁴The Book of Samuel refers to the new moon as chodesh. This implies that an ordinary new moon is called chodesh, and the new moon of Nisan rosh chodesh. Otherwise Samuel would have referred to the new moon by the phrase rosh chodesh.