521. Weekday Prayers on Shabbos

76:19 If one made a mistake at Musaf and started saying the weekday intermediate brachos, he stops in the middle of the bracha where he realized his error and he says the intermediate bracha of Musaf. He does not complete the bracha because there was never a basis to say the weekday intermediate brachos in Musaf, as is the case with the other prayer services of Shabbos.

If a person says a weekday bracha in a Shabbos Amidah, it may be a sign that something about him is not up to par. He should examine his deeds during the following week and rectify his shortcomings.