Hazrat Moulana Ashraf Ali Thaanwi (rahmatullahi ‘alaihi) mentioned:
It is compulsory upon every person to refrain from haraam wealth. However the pious servants of Allah Ta’ala do not confine their caution to refraining from haraam wealth. Rather they exercise extreme caution even in regard to doubtful wealth. By consuming haraam wealth, many evils are created within the soul. This is what destroys man. (Behishti Zewar Pg. 417)
Source: Ihyaauddeen.co.za