One who accepts unlawful money can neither reach a good spiritual position, nor he can have firm beliefs. Unlawful money has many negative consequences. Many people have been experiencing the consequences and one of them is that, they cannot get the answer to their prayers

The Difficulty of Happiness

One, whose prayers are not heard, because of his bad lifestyle & unlawful money, cannot easily gain happiness.

Consequences for Next Generations

People, who accept unlawful money, make their lives and raise their children with it, cannot raise good children either. Such children who are born and raised with unlawful money and food. There is a high chance of them doing haram things when grown up & not being righteous.

Inability to Reach to a High Spiritual Position

One can never reach a good spiritual position if he accepts unlawful money.

Taking away the Beauty of Religious Practitioners

Saying one's prayers can lead him towards the heights of spirituality. But if one accepts unlawful money, his prayers have no meaning anymore. It even becomes harder for such a person to say prayers and to go on fasting.

Regression

According to Quran, one should always move forward; "O thou man! Verily thou art ever toiling on towards thy Lord- painfully toiling,- but thou shalt meet Him."

Some move forward and some move backward. Each step backward gets one closer to the Hell. Both ways are getting people closer to Allah; one via Heaven, and the other one via Hell. One who accepts unlawful money is deviated from the path of Allah, thus, he is moving backward.

Another point to be mentioned is that it does not matter how much unlawful money people use in their lives. According to Prophet (saw), "Even one bite of unlawful food affects one."

Unlawful money, no matter how little it is, belongs to someone else and not us. Therefore, the use of it is not acceptable.