Riddle

Riddle

Shimon is thinking that not long from now he will be doing the mitzva of arbah minim. Of course, he knows that on the 1st day of Succos he cannot use a borrowed set of arbah minim. But Shimon is also thinking that before Succos he will be doing another mitzva, where it will not be proper for him to use his own mitzva item for that mitzva but to borrow it (although his own item is in excellent shape).

Which mitzva is he thinking about?

(Hint: Shimon goes to bed very early.)