Shaykh Abdul Qadir Jilaani Rahmatullah Alayh mentioned: “O people! I realise the state of your wealth when I look at the manner in which it is spent. If I see that the wealth is spent in good avenues I understand that the income was Halaal (lawful). If it was spent in futile and incorrect avenues I deduce that the income was Haraam (unlawful).”
A persian saying reads as:
مال حرام بود ﺑﺠﺎﺋﮯ حرام رفت
(It was Haraam wealth and it was spent in a Haraam avenue.)
Source: Malfoozaat ~Statements and Anecdotes of Faqeeh-Ul-Ummat, Mufti Mahmood Hasan Gangohi Rahmatullah Alayh – Volume 1.