Is there a sin in speaking about worldly matters in the mosque, or not?

Speech in the mosque is divided into two categories: First, if it causes disturbance to those praying, reciting (Qur'an), and studying, then this is not permissible. Second, if it does not cause disturbance: if it is about good matters, then it is good; and if it is about worldly matters, then some of it is prohibited, such as buying and selling, renting, and announcing lost items. What is permissible includes truthful speech that contains nothing forbidden.