Maaseh Rav Siman 24
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
מותר להשתין בתפלין כשהם בראשו בבהכ"ס עראי כמבואר בשו"ע:
Sefaria Community Translation
One may urinate in tefillin when they are on his head in a temporary bathroom as is explained in Shulchan Aruch.