Wa`alykum as-salaamu wa rahmatullahi wa rarakaatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother in Islam, thanks a lot for your question which reflects your care to have a clear view of the teachings of Islam. Allah commands Muslims to refer to people of knowledge to get themselves well-acquainted with the teachings of Islam.
It should be clear that it is strictly forbidden in Islam to cause any interruption or commotion in the masjid because such an act distracts the people who are praying. Thus, it is not allowed to raise funds while people are praying in the masjid. It does not matter if distraction is done by means of voice or action.
The eminent Muslim scholar, Dr. `Abdel-Fattah Idrees, Professor of Comparative Jurisprudence at Al-Azhar Univ., states,
Raising voices in the masjid for any purpose other than dhikr (remembrance of Allah) and prayer is not acceptable. The evidence for this is that the Prophet (peace and blessings be upon him) forbade that the masjid be used for announcing lost items or for business transaction. The reason behind this is that it is forbidden to distract the people from prayer by any means.
Accordingly, despite that raising funds and collecting donations in the masjid is for the common interest of Muslims, voices should not be raised in it to the extent of disturbing the people who are praying, for this is forbidden. Almighty Allah has dispraised unbelievers who used to clap and whistle while Muslims were praying in Al-Masjid Al-Haram; Allah says: “Their prayer at the House (of Allah) is nothing but whistling and clapping of hands: (Its only answer can be), ‘Taste ye the penalty because ye blasphemed.’” (Al-Anfal 8:35) This means that raising voices in the masjid for any purpose other than prayer is forbidden.
Accordingly, we would say that it is forbidden to raise voices in the masjid when people are praying. But when people are not praying, or if the fund-raising campaigns are conducted out of the prayer hall, then it is permissible. You can use some methods to encourage people to give in charity, but try to make sure that you don’t hurt people’s feelings. Also, make sure that you speak in a good manner and don’t turn the masjid into an auction hall.
Allah Almighty knows best.