Praise be to Allaah.
Dirty things are of two types: Things that
are considered dirty or unclean according to sharee’ah because of najaasah
(impurity), such as human urine or faeces, and things that are considered
dirty by people, but they are not naajis according to sharee’ah, such as
mucus and spittle. It is not permissible to carry the former or have them on
one’s person whilst praying or to put them in the mosque; it does not
matter if one carries the latter in one's pocket whilst praying. And Allaah
knows best.