If Shabbos was Erev Rosh Chodesh

Nshei Chabad Newsletter / If Shabbos was Erev Rosh Chodesh and his Shabbos meal continued into the nighttime, he says both R'tzei and Yaale V'yovo in Bentching if he ate at least a K'zayis at nighttime. If he didn't eat a Kezayis at nighttime, he says only R'tzei, unless he davvened Maariv, made Havdoloh, or said Boruch Hamavdil Bein Koidesh L'chol, in which case he says neither R'tzei nor Yaale V'yovo (Likutei Dinei Uminhogei Rosh Chodesh, Ch. 5, Par. 10).