Praise be to Allaah.
Dry impurity does not pass to the one who touches it, so his
garments do not become naajis and neither does his body. If a person sits on
dried urine, his clothes do not become naajis as a result of that, and he
does not have to wash them.
Najaasah (impurity) is only transmitted if it is wet. So if
the impurity is wet or the hand of the one who touches it is wet, then it is
transmitted as a result.
Shaykh Saalih al-Fawzaan (may Allaah preserve him) said:
If a person touches a wet impurity, then he must wash
whatever of it touched his body, because the impurity has been transmitted
to it. But if the impurity is dry, then he does not have to wash the part of
the body that came in contact with it, because it is not transmitted to him.
Shaykh ‘Abd-Allaah ibn ‘Abd al-Rahmaan al-Jibreen (may Allaah
preserve him) was asked:
Does dried urine not make clothes impure? i.e., if a child
urinates on the ground and the urine remains there until it dries without
being washed off, then someone comes and sits on the urine when it has
dried, does his garment becomes impure?
Touching dry impurity does not affect the body or dry
clothes, and it does not matter if one enters a dry washroom with dry feet,
because the impurity is only transmitted when it is wet. End quote.
Fataawa al-Mar’ah al-Muslimah
And Allaah knows best.