116. Forgetting Ya’aleh v’Yavo

19:9 If someone erred during maariv on the first night of Pesach and started saying the weekday Shemoneh Esrei, if he remembered after starting the blessing “bareich aleinu,” he must finish saying that bracha but he does not say tal u’matar since the congregation does not say it on that day. The same is true if the first day to say tal u’matar falls on Shabbos. If someone said a weekday Shemoneh Esrei and realized his error after starting “bareich aleinu,” he would not insert tal u’matar since the congregation is not yet saying it. 19:10 If someone forgot to insert “ya’aleh v’yavo” in shacharis or mincha on Rosh Chodesh, or in any prayer on chol hamoed, if he remembered before the verse “yihiyu l’ratzon” at the end of Shemoneh Esrei, he must return to the beginning of the bracha “r’tzei.” This is true even if he realized his mistake before saying “modim.” (If he remembered before starting modim, he can say it where he remembered – OC 422:1.) If he remembered before concluding the bracha, he can say it at that point and conclude “hamachazir….” If one only remembered after saying “yihiyu l’ratzon,” he must repeat Shemoneh Esrei from the beginning. However, if one forgot to inset ya’aleh v’yavo in maariv on Rosh Chodesh, even on the second day of a two-day Rosh Chodesh, he need not go back or repeat Shemoneh Esrei; this is because the new month was not declared at night.