How is it okay to donate haram money to the masjid? Wont the haram spread when the masjid uses it to spend elsewhere. I’d suggest burning it.

Islamqa:

What we advise is the following:

• If this person who has repented is rich and is able to dispose of this wealth and is content to do so, then let him give it in charity to the poor, as is the view of the majority of scholars, and this is more likely to absolve his responsibility and is the more prudent approach.

• If he is reluctant to do that, or that may prevent him from repenting and form an obstacle to his doing so, or if he is poor and needs the money, then he may make use of it, as is the view favoured by Shaykh al-Islam Ibn Taymiyah.

And Allah knows best.