Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
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.
In this fatwa:
It is allowed to accept suspected money donated by individuals or organizations as long as we are not completely sure it is unlawful (haram).
In response to the question you raised, the European Council for Fatwa and Research (ECFR) issued the following fatwa:
Yes, it is permissible to accept donations from individuals, organizations or governments, whether they be Muslims or non-Muslims, even if we have an over-riding suspicion in the means by which they accumulated their money, unless they donated an item which is explicitly unlawful (haram), such as pork or alcohol.
The majority of scholars believe that this is similar to accepting a gift. However, as soon as these funds become in our possession, they must be used according to the Islamic Shari`ah rules.
In case of a donation from a non-Muslim entity or individual, we must not accept it in the following two circumstances:
First, if this donation leads to the weakening of the ties between the Muslims and their religion and fellow Muslims.
Second, if the donation is subject to conditions which negatively affect the interests of Muslims.
Allah Almighty knows best.