JAMI AL-TIRMIDHI

Concerning urine of a suckling infant before he eats
  (71)

Sayyidah Umm Qays bint Mihsan (RA) said that she took her young son who was not yet
weaned to Allah’s messenger (SAW). He passed urine on the Prophet’s garment, so he
called for water and sprinkled it (on his garment).