Praise be to Allaah.
Mosques are for worship, and it is forbidden to buy, sell and
earn money therein. So it is not permissible to use the mosque as a means of
advertising for companies, schools or anything else.
As for advertisements about religious lectures and seminars,
there is nothing wrong with that, so long as that is not an advertisement
for a specific committee, company, institution or the like. End quote.
From Fataawa al-Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah Aal al-Shaykh (Majallat al-Da’wah, 43)