54. The Black and White Sides of the Straps

10:14 A person should be careful that his tefillin straps have their black sides facing out. If the strap around one's head or arm gets turned white side out, he should fast or give charity. (We are speaking of the strap around the head and the first wrapping that holds the box to the arm, not of the lower parts – see Mishnah Brurah 27:38. The Mishnah Brurah there also calls fasting in such a case an act of piety.) Similarly, if one’s tefillin fell on the ground while outside of their bag, he should fast. If they fall while in the bag, he doesn’t fast but he should donate to charity.

10:15 If a person removes his tefillin in order to go to the bathroom, he must repeat the blessings upon putting them back on. However, from the blessing “Yotzer ohr” (that God creates light) and on, he may not interrupt the prayers to say these blessings. In such case, he should put his tefillin back on without the blessings and, after saying his silent Shemoneh Esrei, touches the tefillin and repeat the blessings.