58. A Person Without Tefillin
10:22 A person who has no tefillin of his own should wait until after the service to borrow a pair. He should then say the Shema and Shemoneh Esrei wearing tefillin instead of praying with the congregation without tefillin. If he is afraid that he will miss the time by which Shema or Shemoneh Esrei must be said, he should then say them without tefillin. If he does this, then when he later gets tefillin, he should say some Tehillim while wearing them, or wear them for the Mincha prayer service. Tefillin are never worn at night. As with a tallis, one may borrow another’s tefillin even without their knowledge, as we assume a person would want to facilitate the performance of a mitzvah through his property.
10:23 Tefillin should only be worn with a clean body, so a person should strive not to pass wind while wearing them. One who must go frequently and unexpectedly to the bathroom does not wear tefillin, since he cannot ensure that he will remain clean. If one believes he can stay clean through the Shema and Shemoneh Esrei, he may wear tefillin. A sick person who is in pain does not wear tefillin because he will not be able to concentrate on them; if he is not in such pain, he wears tefillin. (The Mishnah Brurah says that a sick person in pain may act stringently in this matter and wear tefillin if he chooses but a person with uncontrollable bathroom needs may not opt to put on tefillin – see MB 38:4-5).