הלכה על ראש השנה 56:18

But most of the commentators (Ravad on Mishneh Torah, Rebels 2:9) would say that 'do not add' is only relevant at all with a positive commandment. And the matter according to what I have heard myself from the mouth of my teacher - may God protect him - is, for example, one that lays two fit tefillin on his head or on his arm; and so [too,] one who makes five [sections] in his tefillin; and likewise, one who takes two fit lulavs in his hand and anything similar to it; and so [too,] one who sits in a sukkah (booth) after the holiday with the intention of fulfilling the commandment of sukkah, even though he know that its time has passed - as we only transgress on account of 'do not add' when one has intent to do the commandment - and so [too,] one who takes the lulav after the holiday and has intent to do the commandment while knowing that the holiday has passed. And so is it in the Gemara in Rosh Hashanah 28b in the chapter [entitled] Rauhu Beit Din, as they conclude there, "Rather Rava says, 'To fulfill [a commandment] does not require intent'" - meaning to say that commandments do not require intent - "'to transgress: during its time does not require intent, not in its time requires intent.'" But [in the case of] one who takes the lulav on the holiday, even a hundred times a day, with intention to fulfill [the commandment] each and every time, there is no [issue] of 'do not add'; and so [too,] one who blows the shofar on the day of Rosh Hashanah, and even many times; and so [too,] anything like this. And there is no need to say that there is no [issue of] 'do not add' here, if one takes a disqualified lulav; and so [too] if he grouped a disqualified specie with [a fit lulav], according to the [legal conclusion] - as it is established for us that there is no need for a grouping. This is the general principle of the matter of this prohibition that my teachers, God protect them, distilled from the words of the Gemara after much effort. And now, my son, you too, if you merit and 'eat from the effort of your palms,' 'you will be happy and it will be good for you.'