Question: If one forgets to pray a certain prayer and the time for reciting that prayer has already passed, what is the proper procedure?
Answer: Our Sages taught (Berachot 26b): “One who has erred and has not prayed Shacharit should pray Mincha twice.” This means that if one mistakenly has not prayed one prayer or if one has not prayed a certain prayer because of circumstances beyond one’s control, one must compensate this prayer after having recited the next prayer one prays, for our Sages have established that one must compensate one’s prayer. Thus, if one forgets to pray Shacharit, one should pray Mincha prayers and immediately after doing so, one must recite the Amida prayer again as compensation for the Shacharit prayer which one has missed.
The compensatory prayer applies only to the Amida prayer; however, the rest of the prayer, such as Keri’at Shema and its blessings, Pesukei De’Zimra, and the like, cannot be compensated for and once their time has passed, one has missed out on this Mitzvah.
Thus, one who forgets to pray Shacharit should repeat the Amida immediately after concluding the Mincha prayer and this will compensate for the Shacharit prayer one missed.
The Law Regarding Women
Maran zt”l writes that just as a man who missed a given prayer must compensate for it during the next prayer, so too, a woman who customarily prays a set prayer, such as Shacharit, and it happened that she had forgotten to pray, may likewise compensate for this prayer by reciting the Mincha prayer twice.
Summary: If one forgets to pray any given prayer, such as Shacharit, one must compensate for this prayer after praying Mincha, i.e. after concluding the Mincha Amida prayer, one should wait several seconds and then recite the Amida prayer again in compensation for Shacharit.