We need to study the Shulchan Aruch based on the machloket (dispute) of the Rishonim (early authorities) regarding the following case. Someone is in the middle of the Amidah (standing prayer) and remembers that he already prayed that tefillah (prayer). It could happen: somebody has a minyan kavua (fixed minyan) for Minchah (afternoon prayer), at the regular time before shekiah (sunset), and he was somewhere where they prayed Minchah early. He forgot, goes to Minchah, and in the middle of the Amidah thinks, “I already prayed Minchah.” What does he do? The Rambam says he has to interrupt his Amidah, even in the middle of a Beracha (blessing). He stops in the middle, and that’s it. Why? Because you can’t switch your mind from chovah (obligation) to nedavah. You cannot say, “I had kavanah (intention) to pray my obligation, and in the middle I’m switching my mind to, ‘Oh, okay, this is nedavah.’” You can’t do that.
The Rambam says, but if this was Arvit (evening prayer), he doesn’t interrupt his Amidah. He already prayed Arvit, but he prays Arvit a second time and continues. Since Arvit is not an obligation—meaning it was not an obligation, although we took it as an obligation—lema'aseh (in practice), it’s still in the geder (framework) of reshut (optional), and therefore he could be in the world of nedavah as if he’s giving a present or donation through this tefillah. So the chiddush (novel point) of the Rambam is to make a difference: he says there’s a difference between Arvit and the other tefillot (prayers). In Arvit, if you remember in the middle that you already prayed, you continue the Amidah according to the Rambam.
The Ra'avad, always with his sharp remarks on the Rambam, says, “There’s no Nachat Ruach here; it doesn’t sound good.” That’s all he says. Is halakha (Jewish law) like the Rambam or like the Ra'avad? The truth of the matter is that it’s a very, very complicated thing to impose halakha on. The Magen Avraham comes and says, “I have a proof that halakha is like the Ra'avad.” But even in Arvit, you would have to interrupt your Amidah. Why? Because the Shulchan Aruch, in Siman Kuf Zayin, brings this halakha and doesn’t bring the chiluk (distinction) of the Rambam. He says anybody in the middle of the Amidah who remembers that he already prayed mafsik (interrupts); that’s it. Why doesn’t he say, “But if it’s Arvit, it’s different”? It’s true that this is Hilchot Shacharit (morning prayer), Siman Kuf Zayin; it’s Hilchot Shacharit, but in Hilchot Arvit, it doesn’t bring any difference. In that place, he should have said, “But if it’s Arvit…” So it’s not meforash (explicit), be saying: from the fact that the Shulchan Aruch omits the detail that the Rambam said, the Shulchan Aruch is not mechalek (distinguishes) between Shacharit, Minchah, and Arvit.
Chacham Ovadia brings that there are many places that we still… What’s the sevara (reasoning) of the Ra'avad? The sevara of the Ra'avad is that once you accept Arvit upon yourself to be chovah, to obligation, then it goes back to the same level as everything else. But if we find in halakha that Arvit is still treated as reshut, then even if the Shulchan Aruch was not meforash on this halakha, he would say that he still holds, in the yesod (foundation) of the machloket, like the Rambam: it’s not chovah; it’s reshut. So he goes through that, and at the end, his psak (ruling) halakha is to maintain the psak of the Rambam. Because we do have distinctions between Arvit and the other tefillot, Chacham Ovadia’s psak halakha is like the Rambam, and therefore one has to be very careful.
If somebody prayed Arvit already and then remembers he already prayed, he would have to continue the Amidah, thinking it’s nedavah, and add a little chiddush in that Amidah, a little personal request. But if it were Shacharit or Minchah, one would have to interrupt his Amidah in the moment—the moment he remembers that he already prayed.