Q. A father who was holding his four year old boy while being covered with his Taalis, and the boy made it wet with urine, after it dried can he use it for davening even if it is stained?
A. Poskim maintain that once urine has dried even if the stain could still be seen, whether it is on clothing, floor or furniture. One can recite Tefilos and learn Torah even when facing it.
However, it is proper and a “Hiddur Mitzva” to always wear a clean Taalis and to also daven in a clean shul.
Horav Shlomo Miller’s Shlit’a is similar.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller, Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a