ראש חדש שחל להיו' בשבת ערבי' שחרי' ומנחה מתפלל שבע ואומר יעלה ויבא בעבודה ואינו מזכיר של שבת ביעלה ויבא ומוציאי' שני ספרי' וקורין בראשון שבעה בסדר היום ובשני קורא מפטיר וביום השבת ובראשי חדשיכ' עד סוף הפרש' ומפטירין השמי' כסאי (ואם מזכיר של ר"ח ע"ל סי' רפ"ד ס"ב) חוץ מראש חדש אלול שחל להיות בשבת שמפטירין עניי' סוערה: הגה ויש אומרים השמים כסאי (טור ומרדכי פרק בני העיר ומנהגים) וכן נוהגים במדינות אלו אבל ראש חדש אב שחל להיות בשבת מפטירין שמעו (אבודרהם ומרדכי פ' בני העיר ומנהגים) וי"א השמי' כסאי וכן עיקר במקום שאין מנהג (ת"ה סי' י"ט ומנהגי מהרא"ק) ואם אירע ראש חדש בד' פרשיות מפטירין בשל פרשה (מנהגים) ועיין לקמן סי' תרפ"ה:

When Rosh Ḥodesh falls on Shabbat, for the Maariv, Shacharit and Mincha services pray the regular seven blessings, but say Ya'aleh v-Yavo in the avodah prayer, and it is not necessary to menton Shabbat Ya'aleh v-Yavo. And take out two Torah scrolls, and read from the first the seven regular readings for the day, and from the second, the Maftir reads from “Uviyom HaShabbat uv’Roshei Chodsheichem” until the end of the section. (Numbers 28:9-15). The haftarah is "The heavens are My throne" (Isaiah 66), (and if one mentions Rosh Chodesh there, see Siman 284:2), except for Rosh Ḥodesh Elul that falls on Shabbat, on which we read Isaiah 54:11–55:5, "Unhappy, storm-tossed..." Rema: And some do say Hashamayim Kisi (Isaiah 66), (Tur, Mordechai in Perek Bnei HaIr, and the Minhagim) and this is the custom in our lands. However when Rosh Ḥodesh Av falls on Shabbat some say the haftarah is "Hear ye," (Jeremiah 2:4-28) (Avudraham and Mordechai Perek Bnei HaIr and Minhagim) while others still say "Hashamayim Kisi" (Isaiah 66) and this is the general practice where there is no custom (Terumat HaDeshen Siman 19 and the customs of Maharak). And if Rosh Ḥodesh happens upon one of the four special Shabbatot, we read the final prophetic reading for that reading, and see below, Siman 785.

Rosh Chodesh that falls on the first day of the week, as a final prophetic reading on the Shabbat before it we read I Samuel 20:18-42, "And Jonathan said to him, tomorrow is the new moon" (but we do not override "Unhappy, storm-tossed" or "Hear ye" for the day before Rosh Ḥodesh)(Minhagim). And if Rosh Ḥodesh is two days, Shabbat and Sunday, as a final prophetic reading we read Isaiah 66, "The heavens are My throne," and some have the practice of afterwards reading the first (I Samuel 20:18) and last (I Samuel 20:42) verses of "And Jonathan said to him," to remind that the next day is also Rosh Ḥodesh. Rema: And some say that we do not skip from prophet to prophet, and say nothing but the final prophetic reading for Rosh Ḥodesh. And thus is the custom, but if the final prophetic reading is in the same prophet, we do this and that. If there is a wedding on a Rosh Ḥodesh or on other Sabbaths, we do not override the final prophetic reading.

Rosh Ḥodesh that falls on Shabbat, we include in the musaf the fourth blessing for Shabbat and Rosh Ḥodesh, and conclude it with "who sanctifies the Sabbath and Israel and the new moons."