Halakhah do Samuela I 20:42

Rosh Ḥodesh 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). 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.)