Do the Ahlus-Sunnah wa’l-Jamaa'ah (the mainstream Sunni Muslims) believe that a Muslim who deals in Ribaa (usury or interest) will be in Hell forever? What about Muslim women who do not dress according to the Islamic dress code, or Hijaab, and Muslims who stop praying?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.

Muslims who deal in Ribaa, Muslim women who do not wear Hijab, and Muslims who abandon prayer while believing in it being an obligation are all in violation of Islamic obligations and considered as having committed  grave major sins. However, they would not dwell eternally in Hell if they die while having firm belief in Islamic monotheism, even if they did not repent before their souls reached their throats or the sun rises from the West. In other words, if they are destined to enter Hell, they would not remain there forever; perhaps they would be punished there in proportion to the amount of their sins, unless Allaah The Almighty forgives them.

This is the belief of Ahlus-Sunnah wa’l-Jamaa'ah. The verse in which Allaah The Almighty Says (what means): {So whoever has received an admonition from his Lord and desists may have what is past, and his affair rests with Allaah. But whoever returns to [dealing in interest or usury] - those are the companions of the Fire; they will abide eternally therein.} [Quran 2:275]  does not contradict what has been stated above. This is because it refers to those who deal in usury  and insist that it is not prohibited saying what Allaah The Almighty has warned them about at the beginning of this verse, (which means) {That is because they say, "Trade is [just] like interest."} [Quran 2:275] A Muslim who makes this claim, while being aware of what he says, is guilty of opposing Allaah The Almighty and His laws and is questioning the orders of Allaah The Almighty.

On the other hand, a Muslim who believes that dealing in Ribaa is prohibited, but does it because he is too weak to stop himself is being disobedient. If he dies without repentance, only Allaah the Almighty knows where his destination would end up being.  

Commenting on this verse, Ibn ‘Attiyyah stated that for disbelievers, it should be interpreted to mean eternity in Hell; and for sinning Muslims, it should be interpreted to mean remaining in Hell for a long time.

Allaah Knows best.