Allah says in the Qur'an about the one who consumes riba' as being resurrected as a person inflicted with insanity and having seizures or as a person possessed by demons (may Allah keep us safe from that):
الَّذِينَ يَأْكُلُونَ الرِّبَواْ لاَ يَقُومُونَ إِلاَّ كَمَا يَقُومُ الَّذِى يَتَخَبَّطُهُ الشَّيْطَـنُ مِنَ الْمَسِّ ذَلِكَ بِأَنَّهُمْ قَالُواْ إِنَّمَا الْبَيْعُ مِثْلُ الرِّبَواْ وَأَحَلَّ اللَّهُ الْبَيْعَ وَحَرَّمَ الرِّبَواْ فَمَن جَآءَهُ مَوْعِظَةٌ مِّنْ رَّبِّهِ فَانتَهَى فَلَهُ مَا سَلَفَ وَأَمْرُهُ إِلَى اللَّهِ وَمَنْ عَادَ فَأُوْلَـئِكَ أَصْحَـبُ النَّارِ هُمْ فِيهَا خَـلِدُونَ
Those who eat Riba will not stand (on the Day of Resurrection) except like the standing of a person beaten by Shaytan leading him to insanity. That is because they say: "Trading is only like Riba,'' whereas Allah has permitted trading and forbidden Riba. So whosoever receives an admonition from his Lord and stops eating Riba, shall not be punished for the past; his case is for Allah (to judge); but whoever returns (to Riba), such are the dwellers of the Fire ـ they will Abide therein. (Surah Al-Baqara: 275)
This ayah also shows the Mercy of Allah SWT, that if we repent and get out of it, Allah will forgive, but if one again goes back to this, then he will be among the dwellers of the fire. Someone in the class asked to our Sheikh: What if we already bought a house or a car, and is making payments on it which involves interest (mortgage or where a third party like the bank who has lent the loan is involved)? To this, our Sheikh (may Allah protect him) said: Just sell it off, and then rent etc, if you cannot purchase it with full funds, because nothing in this world is worth the punishment one will have to face in the Hereafter. It is the only sin that is mentioned in the Qur'an that Allah SWT gives notice of war:
يأَيُّهَا الَّذِينَ ءَامَنُواْ اتَّقُواْ اللَّهَ وَذَرُواْ مَا بَقِىَ مِنَ الرِّبَواْ إِن كُنتُمْ مُّؤْمِنِين .فَإِن لَّمْ تَفْعَلُواْ فَأْذَنُواْ بِحَرْبٍ مِّنَ اللَّهِ وَرَسُولِهِ وَإِن تُبتُمْ فَلَكُمْ رُءُوسُ أَمْوَلِكُمْ لاَ تَظْلِمُونَ وَلاَ تُظْلَمُونَ
Oh you who believe! Have Taqwa of Allah and give up what remains from Riba, if you are (really) believers. And if you do not do it, then take a notice of war from Allah and His Messenger but if you repent,you shall have your capital sums. Deal not unjustly, and you shall not be dealt with unjustly. (Surah Al-Baqara: 278, 279)
And Allah says:
وَمَآ ءَاتَيْتُمْ مِّن رِّباً لِّيَرْبُوَاْ فِى أَمْوَالِ النَّاسِ فَلاَ يَرْبُواْ عِندَ اللَّهِ وَمَآ ءاتَيْتُمْ مِّن زَكَوةٍ تُرِيدُونَ وَجْهَ اللَّهِ فَأُوْلَـئِكَ هُمُ الْمُضْعِفُونَ
And that which you give in Riba in order that it may increase from other people's property, has no increase with Allah; but that which you give in Zakah seeking Allah's Face, then those they shall have manifold increase. (Surah Ar-Rum: 39)
Narrated Samura bin Jundab Radhiyallahu anh:
The Prophet Sallallahu alihiwassalam said, "This night I dreamt that two men came and took me to a Holy land whence we proceeded on till we reached a river of blood, where a man was standing, and on its bank was standing another man with stones in his hands. The man in the middle of the river tried to come out, but the other threw a stone in his mouth and forced him to go back to his original place. So, whenever he tried to come out, the other man would throw a stone in his mouth and force him to go back to his former place. I asked, 'Who is this?' I was told, 'The person in the river was a Riba-eater." (Saheeh Al-Bukhari)
All of us see fornication (committing zina) as a major sin. And this is what riba has been compared to. Abdullah ibn Hanjalah related that the Prophet Sallallahu alihiwassalam said: A dirham of Riba (interest) knowingly taken by a man is a sin worse than committing Zina (Imam Ahmad).
Allah ceases to put Barakah in the money of one who deals with riba. So we lose the Blessings of Allah in this world along with the Blessings in The Aakhirah. This is as Allah says:
يَمْحَقُ اللَّهُ الْرِّبَواْ وَيُرْبِى الصَّدَقَـتِ وَاللَّهُ لاَ يُحِبُّ كُلَّ كَفَّارٍ أَثِيمٍ
Allah will deprive usury of all blessing, but will give increase for deeds of charity. (Surah Al-Baqara: 276)
One is prohibited from dealing with interest in any way; be it the one who takes, or gives, the one who writes it and being witnesses for such a transaction. It was narrated that Jaabir Ibn Abdullah Radhiyallahu anh said: “The Messenger of Allaah Sallallahu alihi wassalam cursed the one who consumes ribaa, the one who pays it, the one who writes it down and the two who witness it. He said they are all the same.” (Narrated by Muslim).
It is very clear from the above ayahs and ahaadeeth that dealing with interest is absolutely haram, and a Muslim should stay away from it as much as he can. Whoever is trapped in this big trap, should try to get out of it as soon as possible. Gaining anything in this world by means of interest is not at all worth forsaking our Hereafter. Wa Allahu A'lam.